I found this, but I don't know how where to found the key codes for "WM_KEYDOWN", do you know a list of all the keys transformed for "WM_KEYDOWN"?
[DllImport("User32.Dll", EntryPoint = "PostMessageA", SetLastError = true)]
public static extern bool PostMessage(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam);
PostMessage(winHandle, (uint)WM_KEYDOWN, (IntPtr)66, IntPtr.Zero);