The "edit box" in the copySN.ext program does not have a right click context menu that would allow you to paste the number there by clicking on "paste" in the menu.
You can paste the copied number by using the control+V key.
If nothing appears when you do that, it's likely that you did not copy the number from the original email. Try pasting to a text file. If it doesn't work there, copy the number again. If it pastes to a text file, it should paste to the copySN program as well.
It is better to use the copySN program because it creates the correct file and you don't have to worry about hidden file extensions.
Hook