Thanks Erel. I appreciate you taking the time to look at my code. For program design reasons, I still had to alter your code, since it wasn't allowing for direct execution of built-in Windows programs, such as entering just "notepad" instead of requiring "C:\Windows\Notepad.exe" or entering just "notes" instead of requiring "\Windows\Notes.exe".
Still, not only you gave me the code I needed to launch associated documents, but you also gave me some pointers on how to parse the input, so I think I can now get the code to process URL's too.