How to open a file as binary mode and replace hex strings?

I need open and edit a executable file in binary mode, to replace hex value as string.

In PHP, looks like this:

<?ph开发者_运维知识库p
    $fp = fopen('file.exe', 'r+');
    $content = fread($fp, filesize('file.exe'));
    fclose($fp);
    print $content;
    /* [...] This program cannot be run in DOS mode.[...] */
?>

How I get it in C#?

public void Manipulate()
{
    byte[] data = File.ReadAllBytes("file.exe");
    byte[] newData;

    //walkthrough data and do what you need to do and move to newData

    File.WriteAllBytes("new_file.exe", newData);

}

Use File.ReadAllBytes to read the bytes of a file as a byte array.

byte[] bytes = File.ReadAllBytes('file.exe');

If you want to convert this to a hex string (and I'd in general I'd advise against doing so - strings are immutable in C# so modifying even a single byte will require copying the rest of the string) you can for example use:

string hex = BitConverter.ToString(bytes);

You ask about writting to file, but you PHP code is for reading. For working with files you can use FileStream class

using(FileStream stream = new FileStream(fileName, FileMode.Open, FileAccess.Write))
{
    ....
    stream.WriteByte(byte);
    ....
}