Copying to the clipboard is easy:
Pasting into other applications is harder, if you want to do it directly from C# rather than letting the user do it. You can do it via SendKeys
] but to be honest, that isn't a good practice: if your application started messing with my clipoard just to transfer info to Word or Excel, then I would unistall it with extreme prejudice.
What are you trying to achieve that you think this is a necessary and good idea?