disappearing documents

[Dannor]

Hello,
I've had an annoying adventure today while writing a Pages document. It's a document I've been completing since September, adding a few pages every week. It was stored in a folder in Documents.
So today I was adding some lines as usual. I went away from the computer for a while and when I came back and wanted to continue typing, it wouldn't allow me to. I would get a message "you're not authorised to edit the document" or sth like that. Which is weird as I only have one account.
The thing is, I restarted hoping things would get back to norm - normally even if I close Pages the changes are saved automatically.
Well this time it was different: the document disappeared! I searched with Spotlight, checked Trash, even got a recovery program but there is no sign of the file!
What happened? How can I find it back? It's months worth of work!
Thanks for help

 

[Artimus12]

A disappearing document might point to online activity. But you don't elaborate what you may\may not be signed up to, or what, if any, other devices may be connected to your account.

Think iCloud, Dropbox, OneDrive, etc.

If all else fails and you use Time Machine with any regularity, you may have to do a restore.