When I try to open Word, I get a message that it needs to be updated to Word 365. But when I go to the App Store it indicates that I already have Word 365 installed, and it shows an "Open" button. What do i do next top use Word?

I closed Word and now it won't re-open. I get a message that I need an updated version and I should go to the App Store to get Word 365. But when I go to the App Store, it indicates that I already have 365 installed. But it still won't open. What do I do next? (Word was working fine until this moprning when I started having problems with opening some files. A message said Word did not have permission to open them. If I can get Word to re-open that will be my next question.)