I have created an intricate spreadsheet that I'd like to sell online.
I would like to have the users purchase a product key and have to type
that in before they use the spreadsheet for the first time - like they
were buying regular software. I imagine I'd have to store that
information in a database online so that they can validate their
"copy" of the spreadsheet. Does anyone know if that is a
possibility? I'm afraid of everyone just emailing it to all their
family and friends and so I basically only sell the spreadsheet a few
times and it's distributed freely after that.

Any thoughts? Other solutions you might have experience with?

Thanks!