How can I make an Excel spreadsheet access expire?

I recall a few years ago that I located a program that allowed me to create an Excel spreadsheet and share it with others, but that locked the spreadsheet after a given period of time. I need to create a spreadsheet, but I want to put a time frame on it which requires users to request an access code from me every so many days. I don't want users in my business to be able to take the spreadsheet and use it should they leave the company. I know there was a subscription program that allowed me to do this, but I can't recall the name of it. It also allowed Excel to hide all of the formulas, even though the calculations worked. Does anyone know of this program? Thank you.

Perhaps you may find some info of interest in this link?

https://sites.google.com/site/whitehatxl/

Alf