I would like to be be able to mark an excel file with a key which will come from the system so that when an excel file is imported it would try to find that key to determine if the file came from the system or not. I am currently doing it by specifying the key in the file name but that is very easy to fail. My google-fu is not working, my search results are returning links to adding keys/identification to the cells.

It is not necessarily VB.net but I just posted it here since this forum generates the most attention. It would be in c# but I just want some clues/ideas.

TIA