Thanks, but I did that. Both the quick version and then the long (total reinstall). Still have the same problem.

Repair and reinstall are not the same thing. I accept that you have tried both.
Can you try opening one of the documents on a different system?
What happens if you attempt to encrypt a new document? Does it save? Can you open it?


I believe the encryption algorithm is the same for all of Office, but that is merely a belief. I could not cite any authority for it.

I've tried the short repair, which didn't help, and the online repair twice. Both times the online repair failed with the message Something went wrong, with Error Code 30010-4. Both times, that left my system without Office installed, so I reinstalled Office. I still have the same problem.



I can open the encrypted files on my old Win XP, Word 2007 system, and my Android phone, but Word 365 on Win 10 still crashes when I try to open the files.



I can create a new Word file, password protect it, save and close it in 365, but when I try to reopen it, Word 365 still crashes. The other systems will open the new file.

I also see you are responding to a similar issue on the Microsoft Support pages, and tried your sfc /scannow suggestion, but it did not find any integrity violations.