You'll have to dive into the world of Win32 Unmanaged API. You'll need the following procedures:
- SendMessage - PInvoke.NET - SendMessage
- FindWindow - PInvoke.NET - FindWindow
- FindWindowEx - PInvoke.NET FindWindowEx
- WM_SETTEXT - PInvoke.NET - WM_SETTEXT
The PInvoke links have the .NET Declarations and also provides example usage.
I'm going to give you a text changing example using SendMessage and WM_SETTEXT.
Dim hWnd As Integer = 0
hWnd = FindWindow("notepad", vbNullString) 'Find Notepad
If hWnd = 0 Then
MessageBox.Show("Notepad is not open.")
End If
hWnd = FindWindow(hWnd, 0, "edit", vbNullString) 'Find the Edit Box
SendMessage(hWnd, WM_SETTEXT, 0, "This is my Custom Text!")
This should work, you'll want to use WM_GETTEXT to get the text from the Edit box. Win32 Unmanaged API is something that can be easy to learn if you read the documentation very closely.
Good Luck,
-Allen