MS Word automation with 2 way communication

I am doing embedding of MS Word in my application using Win32 SetParent function. Everything works fine but there is a requirement to do a callback from Word custom toolbar button to parent application. Word instance is embedded in user contr开发者_JAVA百科ol so the parent is this.Handle.

The VBA code looks as follows:

Sub Submit()
Dim hwnd As Long
hwnd = FindWindow("Opusapp", vbNullString)
hwnd = GetAncestor(hwnd, GA_PARENT)
If hwnd = 0 Then
    MsgBox "Failed to callback!"
    Exit Sub
End If
OutputDebugString ("Parent window " + CStr(hwnd))
Dim id As Long
id = RegisterWindowMessage("__CALLBACK_FROM_WORD__")
If hwnd = 0 Then
    MsgBox "Failed to callback. Message not registered"
    Exit Sub
End If
OutputDebugString ("Message " + CStr(id))
End Sub

In C# the code is this:

        protected override void OnHandleCreated(EventArgs e)
    {
        submitMessageId_ = RegisterWindowMessage("__CALLBACK_FROM_WORD__");
        base.OnHandleCreated(e);
    }

    protected override void OnHandleDestroyed(EventArgs e)
    {
        base.OnHandleDestroyed(e);
    }

    protected override void WndProc(ref Message m)
    {
        if (m.Msg == submitMessageId_)
        {
            Logger.Instance().Write("WndProc: Submit event");
            return;
        }
        base.WndProc(ref m);
    }

The problem seems to be that VBA is unable to locate the correct window handle. I tried using GetParent to no avail.

The problem might be, that FindWindow already returns a top-level window (i.e. the one you embedded Word within). IMO there's no need to call GetAncestor, this always returns the desktop window...