I am using the WebBrowser control inside a Windows Form to display a PDF.

Whenever the PDF is regenerated, however, the WebBrowser control only displays its local cached version and not the updated version from the server.

I am using the Refresh() method shown below to try and force the control to reload the PDF, but it doesn't work:

_webBrowser.Navigate(pdfUrl);

_webBrowser.Refresh(WebBrowserRefreshOption.Completely)

Do I have to do开发者_开发百科 anything else to force the refresh to reload the PDF from the server?

Further to Serj Sagan, here is the code with bizarre error handling simplified, the infinite loop removed, and 32/64-bit capable.

/**
* Modified from code originally found here: http://support.microsoft.com/kb/326201
**/
public class WebBrowserHelper
{
    #region Definitions/DLL Imports
    /// <summary>
    /// For PInvoke: Contains information about an entry in the Internet cache
    /// </summary>
    [StructLayout(LayoutKind.Explicit)]
    public struct ExemptDeltaOrReserverd
    {
        [FieldOffset(0)]
        public UInt32 dwReserved;
        [FieldOffset(0)]
        public UInt32 dwExemptDelta;
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct INTERNET_CACHE_ENTRY_INFOA
    {
        public UInt32 dwStructSize;
        public IntPtr lpszSourceUrlName;
        public IntPtr lpszLocalFileName;
        public UInt32 CacheEntryType;
        public UInt32 dwUseCount;
        public UInt32 dwHitRate;
        public UInt32 dwSizeLow;
        public UInt32 dwSizeHigh;
        public FILETIME LastModifiedTime;
        public FILETIME ExpireTime;
        public FILETIME LastAccessTime;
        public FILETIME LastSyncTime;
        public IntPtr lpHeaderInfo;
        public UInt32 dwHeaderInfoSize;
        public IntPtr lpszFileExtension;
        public ExemptDeltaOrReserverd dwExemptDeltaOrReserved;
    }

    // For PInvoke: Initiates the enumeration of the cache groups in the Internet cache
    [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "FindFirstUrlCacheGroup",
        CallingConvention = CallingConvention.StdCall)]
    public static extern IntPtr FindFirstUrlCacheGroup(
        int dwFlags,
        int dwFilter,
        IntPtr lpSearchCondition,
    int dwSearchCondition,
    ref long lpGroupId,
    IntPtr lpReserved);

    // For PInvoke: Retrieves the next cache group in a cache group enumeration
    [DllImport(@"wininet",
    SetLastError = true,
        CharSet = CharSet.Auto,
    EntryPoint = "FindNextUrlCacheGroup",
        CallingConvention = CallingConvention.StdCall)]
    public static extern bool FindNextUrlCacheGroup(
        IntPtr hFind,
        ref long lpGroupId,
        IntPtr lpReserved);

    // For PInvoke: Releases the specified GROUPID and any associated state in the cache index file
    [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "DeleteUrlCacheGroup",
        CallingConvention = CallingConvention.StdCall)]
    public static extern bool DeleteUrlCacheGroup(
        long GroupId,
        int dwFlags,
        IntPtr lpReserved);

    // For PInvoke: Begins the enumeration of the Internet cache
    [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "FindFirstUrlCacheEntryA",
        CallingConvention = CallingConvention.StdCall)]
    public static extern IntPtr FindFirstUrlCacheEntry(
        [MarshalAs(UnmanagedType.LPTStr)] string lpszUrlSearchPattern,
        IntPtr lpFirstCacheEntryInfo,
        ref int lpdwFirstCacheEntryInfoBufferSize);

    // For PInvoke: Retrieves the next entry in the Internet cache
    [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "FindNextUrlCacheEntryA",
        CallingConvention = CallingConvention.StdCall)]
    public static extern bool FindNextUrlCacheEntry(
        IntPtr hFind,
        IntPtr lpNextCacheEntryInfo,
        ref int lpdwNextCacheEntryInfoBufferSize);

    // For PInvoke: Removes the file that is associated with the source name from the cache, if the file exists
    [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "DeleteUrlCacheEntryA",
        CallingConvention = CallingConvention.StdCall)]
    public static extern bool DeleteUrlCacheEntry(
        IntPtr lpszUrlName);
    #endregion

    /// <summary>
    /// Clears the cache of the web browser
    /// </summary>
    public static void ClearCache()
    {
        // Indicates that all of the cache groups in the user's system should be enumerated
        const int CACHEGROUP_SEARCH_ALL = 0x0;
        // Indicates that all the cache entries that are associated with the cache group
        // should be deleted, unless the entry belongs to another cache group.
        const int CACHEGROUP_FLAG_FLUSHURL_ONDELETE = 0x2;
        const int ERROR_INSUFFICIENT_BUFFER = 0x7A;

        // Delete the groups first.
        // Groups may not always exist on the system.
        // For more information, visit the following Microsoft Web site:
        // http://msdn.microsoft.com/library/?url=/workshop/networking/wininet/overview/cache.asp            
        // By default, a URL does not belong to any group. Therefore, that cache may become
        // empty even when the CacheGroup APIs are not used because the existing URL does not belong to any group.            
        long groupId = 0;
        IntPtr enumHandle = FindFirstUrlCacheGroup(0, CACHEGROUP_SEARCH_ALL, IntPtr.Zero, 0, ref groupId, IntPtr.Zero);
        if (enumHandle != IntPtr.Zero) {
            bool more;
            do {
                // Delete a particular Cache Group.
                DeleteUrlCacheGroup(groupId, CACHEGROUP_FLAG_FLUSHURL_ONDELETE, IntPtr.Zero);
                more = FindNextUrlCacheGroup(enumHandle, ref groupId, IntPtr.Zero);
            } while (more);
        }

        // Start to delete URLs that do not belong to any group.
        int cacheEntryInfoBufferSizeInitial = 0;
        FindFirstUrlCacheEntry(null, IntPtr.Zero, ref cacheEntryInfoBufferSizeInitial);  // should always fail because buffer is too small
        if (Marshal.GetLastWin32Error() == ERROR_INSUFFICIENT_BUFFER) {
            int cacheEntryInfoBufferSize = cacheEntryInfoBufferSizeInitial;
            IntPtr cacheEntryInfoBuffer = Marshal.AllocHGlobal(cacheEntryInfoBufferSize);
            enumHandle = FindFirstUrlCacheEntry(null, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);
            if (enumHandle != IntPtr.Zero) {
                bool more;
                do {
                    INTERNET_CACHE_ENTRY_INFOA internetCacheEntry = (INTERNET_CACHE_ENTRY_INFOA)Marshal.PtrToStructure(cacheEntryInfoBuffer, typeof(INTERNET_CACHE_ENTRY_INFOA));
                    cacheEntryInfoBufferSizeInitial = cacheEntryInfoBufferSize;
                    DeleteUrlCacheEntry(internetCacheEntry.lpszSourceUrlName);
                    more = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);
                    if (!more && Marshal.GetLastWin32Error() == ERROR_INSUFFICIENT_BUFFER) {
                        cacheEntryInfoBufferSize = cacheEntryInfoBufferSizeInitial;
                        cacheEntryInfoBuffer = Marshal.ReAllocHGlobal(cacheEntryInfoBuffer, (IntPtr)cacheEntryInfoBufferSize);
                        more = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);
                    }
                } while (more);
            }
            Marshal.FreeHGlobal(cacheEntryInfoBuffer);
        }
    }
}

Sheng Jiang is correct - you need the programmatically clear IE's cache. Here is sample code showing how to do this in c#: http://www.gutgames.com/post/Clearing-the-Cache-of-a-WebBrowser-Control.aspx

Copy in case the page goes offline:

/**
* Modified from code originally found here: 
http://support.microsoft.com/kb/326201
**/

#region Usings
using System;
using System.Runtime.InteropServices;

#endregion

namespace Utilities.Web.WebBrowserHelper
{
    /// <summary>
    /// Class for clearing the cache
    /// </summary>
    public static class WebBrowserHelper
    {
        #region Definitions/DLL Imports
        /// <summary>
        /// For PInvoke: Contains information about an entry in the Internet cache
        /// </summary>
        [StructLayout(LayoutKind.Explicit, Size = 80)]
        public struct INTERNET_CACHE_ENTRY_INFOA
        {
            [FieldOffset(0)]
            public uint dwStructSize;
            [FieldOffset(4)]
            public IntPtr lpszSourceUrlName;
            [FieldOffset(8)]
            public IntPtr lpszLocalFileName;
            [FieldOffset(12)]
            public uint CacheEntryType;
            [FieldOffset(16)]
            public uint dwUseCount;
            [FieldOffset(20)]
            public uint dwHitRate;
            [FieldOffset(24)]
            public uint dwSizeLow;
            [FieldOffset(28)]
            public uint dwSizeHigh;
            [FieldOffset(32)]
            public System.Runtime.InteropServices.ComTypes.FILETIME LastModifiedTime;
            [FieldOffset(40)]
            public System.Runtime.InteropServices.ComTypes.FILETIME ExpireTime;
            [FieldOffset(48)]
            public System.Runtime.InteropServices.ComTypes.FILETIME LastAccessTime;
            [FieldOffset(56)]
            public System.Runtime.InteropServices.ComTypes.FILETIME LastSyncTime;
            [FieldOffset(64)]
            public IntPtr lpHeaderInfo;
            [FieldOffset(68)]
            public uint dwHeaderInfoSize;
            [FieldOffset(72)]
            public IntPtr lpszFileExtension;
            [FieldOffset(76)]
            public uint dwReserved;
            [FieldOffset(76)]
            public uint dwExemptDelta;
        }

        // For PInvoke: Initiates the enumeration of the cache groups in the Internet cache
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "FindFirstUrlCacheGroup",
        CallingConvention = CallingConvention.StdCall)]
        public static extern IntPtr FindFirstUrlCacheGroup(
        int dwFlags,
        int dwFilter,
        IntPtr lpSearchCondition,
        int dwSearchCondition,
        ref long lpGroupId,
        IntPtr lpReserved);

        // For PInvoke: Retrieves the next cache group in a cache group enumeration
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "FindNextUrlCacheGroup",
        CallingConvention = CallingConvention.StdCall)]
        public static extern bool FindNextUrlCacheGroup(
        IntPtr hFind,
        ref long lpGroupId,
        IntPtr lpReserved);

        // For PInvoke: Releases the specified GROUPID and any associated state in the cache index file
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "DeleteUrlCacheGroup",
        CallingConvention = CallingConvention.StdCall)]
        public static extern bool DeleteUrlCacheGroup(
        long GroupId,
        int dwFlags,
        IntPtr lpReserved);

        // For PInvoke: Begins the enumeration of the Internet cache
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "FindFirstUrlCacheEntryA",
        CallingConvention = CallingConvention.StdCall)]
        public static extern IntPtr FindFirstUrlCacheEntry(
        [MarshalAs(UnmanagedType.LPTStr)] string lpszUrlSearchPattern,
        IntPtr lpFirstCacheEntryInfo,
        ref int lpdwFirstCacheEntryInfoBufferSize);

        // For PInvoke: Retrieves the next entry in the Internet cache
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "FindNextUrlCacheEntryA",
        CallingConvention = CallingConvention.StdCall)]
        public static extern bool FindNextUrlCacheEntry(
        IntPtr hFind,
        IntPtr lpNextCacheEntryInfo,
        ref int lpdwNextCacheEntryInfoBufferSize);

        // For PInvoke: Removes the file that is associated with the source name from the cache, if the file exists
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "DeleteUrlCacheEntryA",
        CallingConvention = CallingConvention.StdCall)]
        public static extern bool DeleteUrlCacheEntry(
        IntPtr lpszUrlName);
        #endregion

        #region Public Static Functions

        /// <summary>
        /// Clears the cache of the web browser
        /// </summary>
        public static void ClearCache()
        {
            // Indicates that all of the cache groups in the user's system should be enumerated
            const int CACHEGROUP_SEARCH_ALL = 0x0;
            // Indicates that all the cache entries that are associated with the cache group
            // should be deleted, unless the entry belongs to another cache group.
            const int CACHEGROUP_FLAG_FLUSHURL_ONDELETE = 0x2;
            // File not found.
            const int ERROR_FILE_NOT_FOUND = 0x2;
            // No more items have been found.
            const int ERROR_NO_MORE_ITEMS = 259;
            // Pointer to a GROUPID variable
            long groupId = 0;

            // Local variables
            int cacheEntryInfoBufferSizeInitial = 0;
            int cacheEntryInfoBufferSize = 0;
            IntPtr cacheEntryInfoBuffer = IntPtr.Zero;
            INTERNET_CACHE_ENTRY_INFOA internetCacheEntry;
            IntPtr enumHandle = IntPtr.Zero;
            bool returnValue = false;

            // Delete the groups first.
            // Groups may not always exist on the system.
            // For more information, visit the following Microsoft Web site:
            // http://msdn.microsoft.com/library/?url=/workshop/networking/wininet/overview/cache.asp            
            // By default, a URL does not belong to any group. Therefore, that cache may become
            // empty even when the CacheGroup APIs are not used because the existing URL does not belong to any group.            
            enumHandle = FindFirstUrlCacheGroup(0, CACHEGROUP_SEARCH_ALL, IntPtr.Zero, 0, ref groupId, IntPtr.Zero);
            // If there are no items in the Cache, you are finished.
            if (enumHandle != IntPtr.Zero && ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error())
                return;

            // Loop through Cache Group, and then delete entries.
            while (true)
            {
                if (ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error() || ERROR_FILE_NOT_FOUND == Marshal.GetLastWin32Error()) { break; }
                // Delete a particular Cache Group.
                returnValue = DeleteUrlCacheGroup(groupId, CACHEGROUP_FLAG_FLUSHURL_ONDELETE, IntPtr.Zero);
                if (!returnValue && ERROR_FILE_NOT_FOUND == Marshal.GetLastWin32Error())
                {
                    returnValue = FindNextUrlCacheGroup(enumHandle, ref groupId, IntPtr.Zero);
                }

                if (!returnValue && (ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error() || ERROR_FILE_NOT_FOUND == Marshal.GetLastWin32Error()))
                    break;
            }

            // Start to delete URLs that do not belong to any group.
            enumHandle = FindFirstUrlCacheEntry(null, IntPtr.Zero, ref cacheEntryInfoBufferSizeInitial);
            if (enumHandle != IntPtr.Zero && ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error())
                return;

            cacheEntryInfoBufferSize = cacheEntryInfoBufferSizeInitial;
            cacheEntryInfoBuffer = Marshal.AllocHGlobal(cacheEntryInfoBufferSize);
            enumHandle = FindFirstUrlCacheEntry(null, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);

            while (true)
            {
                internetCacheEntry = (INTERNET_CACHE_ENTRY_INFOA)Marshal.PtrToStructure(cacheEntryInfoBuffer, typeof(INTERNET_CACHE_ENTRY_INFOA));
                if (ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error()) { break; }

                cacheEntryInfoBufferSizeInitial = cacheEntryInfoBufferSize;
                returnValue = DeleteUrlCacheEntry(internetCacheEntry.lpszSourceUrlName);
                if (!returnValue)
                {
                    returnValue = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);
                }
                if (!returnValue && ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error())
                {
                    break;
                }
                if (!returnValue && cacheEntryInfoBufferSizeInitial > cacheEntryInfoBufferSize)
            {
                    cacheEntryInfoBufferSize = cacheEntryInfoBufferSizeInitial;
                    cacheEntryInfoBuffer = Marshal.ReAllocHGlobal(cacheEntryInfoBuffer, (IntPtr)cacheEntryInfoBufferSize);
                    returnValue = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);
                }
            }
            Marshal.FreeHGlobal(cacheEntryInfoBuffer);
        }
        #endregion
    }
}

It is based heavily on the Microsoft KB article here: http://support.microsoft.com/kb/326201

And to pre-empt the question - yes this is a huge pain in the neck, and no, there isn't another way around it. Good luck!

This is an extension to Chris Clark's answer... this code is too important, I figure stack overflow is a more secure place to keep it, plus I got rid of the line numbers for you. Here's a link to the original article again: http://www.gutgames.com/post/Clearing-the-Cache-of-a-WebBrowser-Control.aspx

And the code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;

namespace Utilities.Web.WebBrowserHelper
{
    /**
    * Modified from code originally found here: http://support.microsoft.com/kb/326201
    **/
    public class WebBrowserHelper
    {
        #region Definitions/DLL Imports
        /// <summary>
        /// For PInvoke: Contains information about an entry in the Internet cache
        /// </summary>
        [StructLayout(LayoutKind.Explicit, Size = 80)]
        public struct INTERNET_CACHE_ENTRY_INFOA
        {
            [FieldOffset(0)]
            public uint dwStructSize;
            [FieldOffset(4)]
            public IntPtr lpszSourceUrlName;
            [FieldOffset(8)]
            public IntPtr lpszLocalFileName;
            [FieldOffset(12)]
            public uint CacheEntryType;
            [FieldOffset(16)]
            public uint dwUseCount;
            [FieldOffset(20)]
            public uint dwHitRate;
            [FieldOffset(24)]
            public uint dwSizeLow;
            [FieldOffset(28)]
            public uint dwSizeHigh;
            [FieldOffset(32)]
            public System.Runtime.InteropServices.ComTypes.FILETIME LastModifiedTime;
            [FieldOffset(40)]
            public System.Runtime.InteropServices.ComTypes.FILETIME ExpireTime;
            [FieldOffset(48)]
            public System.Runtime.InteropServices.ComTypes.FILETIME LastAccessTime;
            [FieldOffset(56)]
            public System.Runtime.InteropServices.ComTypes.FILETIME LastSyncTime;
            [FieldOffset(64)]
            public IntPtr lpHeaderInfo;
            [FieldOffset(68)]
            public uint dwHeaderInfoSize;
            [FieldOffset(72)]
            public IntPtr lpszFileExtension;
            [FieldOffset(76)]
            public uint dwReserved;
            [FieldOffset(76)]
            public uint dwExemptDelta;
        }

        // For PInvoke: Initiates the enumeration of the cache groups in the Internet cache
        [DllImport(@"wininet",
            SetLastError = true,
            CharSet = CharSet.Auto,
            EntryPoint = "FindFirstUrlCacheGroup",
            CallingConvention = CallingConvention.StdCall)]
        public static extern IntPtr FindFirstUrlCacheGroup(
            int dwFlags,
            int dwFilter,
            IntPtr lpSearchCondition,
        int dwSearchCondition,
        ref long lpGroupId,
        IntPtr lpReserved);

        // For PInvoke: Retrieves the next cache group in a cache group enumeration
        [DllImport(@"wininet",
        SetLastError = true,
            CharSet = CharSet.Auto,
        EntryPoint = "FindNextUrlCacheGroup",
            CallingConvention = CallingConvention.StdCall)]
        public static extern bool FindNextUrlCacheGroup(
            IntPtr hFind,
            ref long lpGroupId,
            IntPtr lpReserved);

        // For PInvoke: Releases the specified GROUPID and any associated state in the cache index file
        [DllImport(@"wininet",
            SetLastError = true,
            CharSet = CharSet.Auto,
            EntryPoint = "DeleteUrlCacheGroup",
            CallingConvention = CallingConvention.StdCall)]
        public static extern bool DeleteUrlCacheGroup(
            long GroupId,
            int dwFlags,
            IntPtr lpReserved);

        // For PInvoke: Begins the enumeration of the Internet cache
        [DllImport(@"wininet",
            SetLastError = true,
            CharSet = CharSet.Auto,
            EntryPoint = "FindFirstUrlCacheEntryA",
            CallingConvention = CallingConvention.StdCall)]
        public static extern IntPtr FindFirstUrlCacheEntry(
            [MarshalAs(UnmanagedType.LPTStr)] string lpszUrlSearchPattern,
            IntPtr lpFirstCacheEntryInfo,
            ref int lpdwFirstCacheEntryInfoBufferSize);

        // For PInvoke: Retrieves the next entry in the Internet cache
        [DllImport(@"wininet",
            SetLastError = true,
            CharSet = CharSet.Auto,
            EntryPoint = "FindNextUrlCacheEntryA",
            CallingConvention = CallingConvention.StdCall)]
        public static extern bool FindNextUrlCacheEntry(
            IntPtr hFind,
            IntPtr lpNextCacheEntryInfo,
            ref int lpdwNextCacheEntryInfoBufferSize);

        // For PInvoke: Removes the file that is associated with the source name from the cache, if the file exists
        [DllImport(@"wininet",
            SetLastError = true,
            CharSet = CharSet.Auto,
            EntryPoint = "DeleteUrlCacheEntryA",
            CallingConvention = CallingConvention.StdCall)]
        public static extern bool DeleteUrlCacheEntry(
            IntPtr lpszUrlName);
        #endregion

        #region Public Static Functions

        /// <summary>
        /// Clears the cache of the web browser
        /// </summary>
        public static void ClearCache()
        {
            // Indicates that all of the cache groups in the user's system should be enumerated
            const int CACHEGROUP_SEARCH_ALL = 0x0;
            // Indicates that all the cache entries that are associated with the cache group
            // should be deleted, unless the entry belongs to another cache group.
            const int CACHEGROUP_FLAG_FLUSHURL_ONDELETE = 0x2;
            // File not found.
            const int ERROR_FILE_NOT_FOUND = 0x2;
            // No more items have been found.
            const int ERROR_NO_MORE_ITEMS = 259;
            // Pointer to a GROUPID variable
            long groupId = 0;

            // Local variables
            int cacheEntryInfoBufferSizeInitial = 0;
            int cacheEntryInfoBufferSize = 0;
            IntPtr cacheEntryInfoBuffer = IntPtr.Zero;
            INTERNET_CACHE_ENTRY_INFOA internetCacheEntry;
            IntPtr enumHandle = IntPtr.Zero;
            bool returnValue = false;

            // Delete the groups first.
            // Groups may not always exist on the system.
            // For more information, visit the following Microsoft Web site:
            // http://msdn.microsoft.com/library/?url=/workshop/networking/wininet/overview/cache.asp            
            // By default, a URL does not belong to any group. Therefore, that cache may become
            // empty even when the CacheGroup APIs are not used because the existing URL does not belong to any group.            
            enumHandle = FindFirstUrlCacheGroup(0, CACHEGROUP_SEARCH_ALL, IntPtr.Zero, 0, ref groupId, IntPtr.Zero);
            // If there are no items in the Cache, you are finished.
            if (enumHandle != IntPtr.Zero && ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error())
                return;

            // Loop through Cache Group, and then delete entries.
            while (true)
            {
                if (ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error() || ERROR_FILE_NOT_FOUND == Marshal.GetLastWin32Error()) { break; }
                // Delete a particular Cache Group.
                returnValue = DeleteUrlCacheGroup(groupId, CACHEGROUP_FLAG_FLUSHURL_ONDELETE, IntPtr.Zero);
                if (!returnValue && ERROR_FILE_NOT_FOUND == Marshal.GetLastWin32Error())
                {
                    returnValue = FindNextUrlCacheGroup(enumHandle, ref groupId, IntPtr.Zero);
                }

                if (!returnValue && (ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error() || ERROR_FILE_NOT_FOUND == Marshal.GetLastWin32Error()))
                    break;
            }

            // Start to delete URLs that do not belong to any group.
            enumHandle = FindFirstUrlCacheEntry(null, IntPtr.Zero, ref cacheEntryInfoBufferSizeInitial);
            if (enumHandle != IntPtr.Zero && ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error())
                return;

            cacheEntryInfoBufferSize = cacheEntryInfoBufferSizeInitial;
            cacheEntryInfoBuffer = Marshal.AllocHGlobal(cacheEntryInfoBufferSize);
            enumHandle = FindFirstUrlCacheEntry(null, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);

            while (true)
            {
                internetCacheEntry = (INTERNET_CACHE_ENTRY_INFOA)Marshal.PtrToStructure(cacheEntryInfoBuffer, typeof(INTERNET_CACHE_ENTRY_INFOA));
                if (ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error()) { break; }

                cacheEntryInfoBufferSizeInitial = cacheEntryInfoBufferSize;
                returnValue = DeleteUrlCacheEntry(internetCacheEntry.lpszSourceUrlName);
                if (!returnValue)
                {
                    returnValue = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);
                }
                if (!returnValue && ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error())
                {
                    break;
                }
                if (!returnValue && cacheEntryInfoBufferSizeInitial > cacheEntryInfoBufferSize)
                {
                    cacheEntryInfoBufferSize = cacheEntryInfoBufferSizeInitial;
                    cacheEntryInfoBuffer = Marshal.ReAllocHGlobal(cacheEntryInfoBuffer, (IntPtr)cacheEntryInfoBufferSize);
                    returnValue = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);
                }
            }
            Marshal.FreeHGlobal(cacheEntryInfoBuffer);
        }
        #endregion
    }
}

Since WebBrowser (actually IE's Trident engine) use WinInet for networking, you can use WinInet's cache management APIs to remove the cached files before navigating.

Add to the url a random id so the url is unique every time

We found that completely clearing the cache takes too long. An alternative that seems to work well (and fixes the problem in the original question of Refresh not working) is to move the call to Refresh after the document has finished loading.

webBrowser.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(OnWebBrowserDocumentCompleted);

// ...

private void OnWebBrowserDocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
    if (cacheIsStale)
    {
        webBrowser.Refresh(WebBrowserRefreshOption.Completely);
    }
}

How to determine the value of cacheIsStale will depend on your application.

To Prevent CSS caching you can use a sneaky trick when including the css file:

<link type="text/css" href="css/outlook.css?<?php echo date('l jS \of F Y h:i:s A'); ?>" rel="stylesheet" />

It downloads a new copy of the css because the ?date_stuff changes every time.

Is the PDF being embedded with an object tag or something? If so, asking the browser object to refresh won't have any effect- you have to script the PDF viewer to do the refresh (eg, get ahold of the PDF viewer object by ID from the webbrowser control), since that's what downloaded it.

Vescan Petru is on the right track I think. Clearing the IE browser caches is pretty heavy handed and not user friendly. Adapting the suggested MS code linked by Chris Clark to just clear the specific file from the cache looks an interesting bit of code to work on but the simplest answer would be to grab a new temporary file name and then make a copy of the target PDF file with that name. Then display the temp file - deleting it upon exit.

That is my working solution implemented when I hit the same problem.

For those of us who still need to write VB.NET, I ported the code posted by Serj Sagan and Oliver Bock above to VB and found that it works well.

Thank goodness this thread exists, I was really sweating this issue for a long while.

        '
    ' Modified from code originally found here: http://support.microsoft.com/kb/326201
    '
    Public Class WebBrowserHelper

Region "Definitions/DLL Imports"

        ''' <summary>
        ''' For PInvoke: Contains information about an entry In the Internet cache
        ''' </summary>
        <StructLayout(LayoutKind.Explicit)>
        Public Structure ExemptDeltaOrReserverd
            <FieldOffset(0)>
            Public dwReserved As UInt32
            <FieldOffset(0)>
            Public dwExemptDelta As UInt32
        End Structure

        <StructLayout(LayoutKind.Sequential)>
        Public Structure INTERNET_CACHE_ENTRY_INFOA
            Public dwStructSize As UInt32
            Public lpszSourceUrlName As IntPtr
            Public lpszLocalFileName As IntPtr
            Public CacheEntryType As UInt32
            Public dwUseCount As UInt32
            Public dwHitRate As UInt32
            Public dwSizeLow As UInt32
            Public dwSizeHigh As UInt32
            Public LastModifiedTime As FILETIME
            Public ExpireTime As FILETIME
            Public LastAccessTime As FILETIME
            Public LastSyncTime As FILETIME
            Public lpHeaderInfo As IntPtr
            Public dwHeaderInfoSize As UInt32
            Public lpszFileExtension As IntPtr
            Public dwExemptDeltaOrReserved As ExemptDeltaOrReserverd
        End Structure

        ' For PInvoke: Initiates the enumeration Of the cache groups In the Internet cache
        <DllImport("wininet", SetLastError:=True, CharSet:=CharSet.Auto, EntryPoint:="FindFirstUrlCacheGroup", CallingConvention:=CallingConvention.StdCall)>
        Public Shared Function FindFirstUrlCacheGroup(dwFlags As Integer, dwFilter As Integer, lpSearchCondition As IntPtr, dwSearchCondition As Integer, ByRef lpGroupId As Long,
                            lpReserved As IntPtr) As IntPtr
        End Function

        ' For PInvoke: Retrieves the Next cache group In a cache group enumeration
        <DllImport("wininet", SetLastError:=True, CharSet:=CharSet.Auto, EntryPoint:="FindNextUrlCacheGroup", CallingConvention:=CallingConvention.StdCall)>
        Public Shared Function FindNextUrlCacheGroup(hFind As IntPtr, ByRef lpGroupId As Long, lpReserved As IntPtr) As Boolean
        End Function

        ' For PInvoke: Releases the specified GROUPID And any associated state In the cache index file
        <DllImport("wininet", SetLastError:=True, CharSet:=CharSet.Auto, EntryPoint:="DeleteUrlCacheGroup", CallingConvention:=CallingConvention.StdCall)>
        Public Shared Function DeleteUrlCacheGroup(GroupId As Long, dwFlags As Integer, lpReserved As IntPtr) As Boolean
        End Function

        ' For PInvoke: Begins the enumeration Of the Internet cache
        <DllImport("wininet", SetLastError:=True, CharSet:=CharSet.Auto, EntryPoint:="FindFirstUrlCacheEntryA", CallingConvention:=CallingConvention.StdCall)>
        Public Shared Function FindFirstUrlCacheEntry(<MarshalAs(UnmanagedType.LPTStr)> lpszUrlSearchPattern As String, lpFirstCacheEntryInfo As IntPtr,
                                                      ByRef lpdwFirstCacheEntryInfoBufferSize As Integer) As IntPtr
        End Function

        ' For PInvoke: Retrieves the Next entry In the Internet cache
        <DllImport("wininet", SetLastError:=True, CharSet:=CharSet.Auto, EntryPoint:="FindNextUrlCacheEntryA", CallingConvention:=CallingConvention.StdCall)>
        Public Shared Function FindNextUrlCacheEntry(hFind As IntPtr, lpNextCacheEntryInfo As IntPtr, ByRef lpdwNextCacheEntryInfoBufferSize As Integer) As Boolean
        End Function

        ' For PInvoke: Removes the file that Is associated With the source name from the cache, If the file exists
        <DllImport("wininet", SetLastError:=True, CharSet:=CharSet.Auto, EntryPoint:="DeleteUrlCacheEntryA", CallingConvention:=CallingConvention.StdCall)>
        Public Shared Function DeleteUrlCacheEntry(lpszUrlName As IntPtr) As Boolean
        End Function

End Region

        ''' <summary>
        ''' Clears the cache of the web browser
        ''' </summary>
        Public Shared Sub ClearCache()
            ' Indicates that all of the cache groups in the user's system should be enumerated
            Const CACHEGROUP_SEARCH_ALL As Integer = &H0
            ' Indicates that all the cache entries that are associated with the cache group
            ' should be deleted, unless the entry belongs to another cache group.
            Const CACHEGROUP_FLAG_FLUSHURL_ONDELETE As Integer = &H2
            Const ERROR_INSUFFICIENT_BUFFER As Integer = &H7A

            ' Delete the groups first.
            ' Groups may Not always exist on the system.
            ' For more information, visit the following Microsoft Web site:
            ' http//msdn.microsoft.com/library/?url=/workshop/networking/wininet/overview/cache.asp            
            ' By default, a URL does Not belong to any group. Therefore, that cache may become
            ' empty even when the CacheGroup APIs are Not used because the existing URL does Not belong to any group.            
            Dim groupId As Long = 0
            Dim enumHandle As IntPtr = FindFirstUrlCacheGroup(0, CACHEGROUP_SEARCH_ALL, IntPtr.Zero, 0, groupId, IntPtr.Zero)

            If (enumHandle <> IntPtr.Zero) Then
                Dim more As Boolean

                Do
                    ' Delete a particular Cache Group.
                    DeleteUrlCacheGroup(groupId, CACHEGROUP_FLAG_FLUSHURL_ONDELETE, IntPtr.Zero)
                    more = FindNextUrlCacheGroup(enumHandle, groupId, IntPtr.Zero)
                Loop While (more)
            End If

            ' Start to delete URLs that do Not belong to any group.
            Dim cacheEntryInfoBufferSizeInitial As Integer = 0

            FindFirstUrlCacheEntry(Nothing, IntPtr.Zero, cacheEntryInfoBufferSizeInitial)  ' should always fail because buffer Is too small

            If Marshal.GetLastWin32Error() = ERROR_INSUFFICIENT_BUFFER Then
                Dim cacheEntryInfoBufferSize As Integer = cacheEntryInfoBufferSizeInitial
                Dim cacheEntryInfoBuffer As IntPtr = Marshal.AllocHGlobal(cacheEntryInfoBufferSize)

                enumHandle = FindFirstUrlCacheEntry(Nothing, cacheEntryInfoBuffer, cacheEntryInfoBufferSizeInitial)

                If (enumHandle <> IntPtr.Zero) Then
                    Dim more As Boolean
                    Do
                        Dim internetCacheEntry As INTERNET_CACHE_ENTRY_INFOA = CType(Marshal.PtrToStructure(cacheEntryInfoBuffer, GetType(INTERNET_CACHE_ENTRY_INFOA)), INTERNET_CACHE_ENTRY_INFOA)

                        cacheEntryInfoBufferSizeInitial = cacheEntryInfoBufferSize
                        DeleteUrlCacheEntry(internetCacheEntry.lpszSourceUrlName)
                        more = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, cacheEntryInfoBufferSizeInitial)

                        If Not more AndAlso Marshal.GetLastWin32Error() = ERROR_INSUFFICIENT_BUFFER Then
                            cacheEntryInfoBufferSize = cacheEntryInfoBufferSizeInitial
                            cacheEntryInfoBuffer = Marshal.ReAllocHGlobal(cacheEntryInfoBuffer, CType(cacheEntryInfoBufferSize, IntPtr))
                            more = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, cacheEntryInfoBufferSizeInitial)
                        End If
                    Loop While (more)
                End If

                Marshal.FreeHGlobal(cacheEntryInfoBuffer)
            End If
        End Sub
    End Class

TimeSpan serialNoCache = DateTime.Now.TimeOfDay;
string urlNocache = string.Format("{0}?v={1}", "https://www.google.com/", serialNoCache.ToString());
this.webBrowser.Navigate(urlNocache);