Sending simulated keystrokes to Directx games via WPF application

I don't think this can be related to DirectX. If you want to trick some existing games and other applications, all you can do is to use the raw Windows API method SendInput:
http://msdn.microsoft.com/en-us/library/windows/desktop/ms646310%28v=vs.85%29.aspx[^].

This is how it can be used in a .NET application via P/Invoke: http://www.pinvoke.net/default.aspx/user32.sendinput[^].

See also:
http://en.wikipedia.org/wiki/P/Invoke[^],
http://msdn.microsoft.com/library/en-us/vcmxspec/html/vcmg_PlatformInvocationServices.asp[^].

This is really low-level API, the same or similar to what hardware drivers use in their implementations. Nothing else will work in all cases. Also, you should understand that you should not use it for UI development. It can only be used for playing tricks on applications which won't provide any other kind of collaboration; other examples include creation of UI testing software or playing back of keyboard and/or mouse macro. For UI development, it would be pure and very impractical abuse.

—SA