I have two applications, App1 and App2

App1 can send a message to App2 and change App2's caption so I know I have the correct handle to App2 so why can I not subclass App2 from App1 using App2's handle

I have a working WndProc in App1 and it can subclass App1 using App1's handle but if I change the handle to App2's handle it wont catch messages from App2

Can it be done