File format invalid for Pages document
I have recently updated to Monterey and have Pages 11.2. I have a Pages document (Internet Logons) that I use every day and last updated on 7th October 2021. After the update to Monterey, Pages cannot open the document and displays "Internet Logons.pages" can't be opened right now. The file format is invalid.
I have restored copies of the file from Time Machine from before 7th October and still same message. The file was perfectly usable before updating to Monterey.
Maybe Pages 11.2 is at fault - is it possible to revert to an earlier version?
Mac Pro, macOS 12.0