I have a MacBook air from 2015 and as of this morning I have not been able to save my Word documents (Word 2016). I've never had issues before.
When I press save on a new document, a message pops up saying, "The file “Documents” couldn’t be opened." Why is this happening?
Sounds like you haven't granted Word permission to access your ~/Documents folder. Check in System Preferences > Security & Privacy > Privacy tab and see if Microsoft Word is listed in the Files and Folders section with any unchecked items. You can also try adding it to the Full Disk Access area.
If that doesn't work, you might be looking at a more general permissions problem with your Home folder. In that case https://support.apple.com/en-us/HT203538 is worth checking out. Good luck!
Since you have mentioned, I've never had issues before, I am assuming all your permissions are correctly placed.
So, it could be that the temporary (recovery) file that Word creates for every document is damaged or that the preference file for MS Word is also damaged. The former is here:
/Users/<username>/Library/Containers/com.microsoft.Word/Data/Library/Preferences/AutoRecovery.
The latter is here:
~/Library/Preferences/com.microsoft.Word.plist
Trash all the auto-recovery files and trash the .plist file and launch MS Word again. That should fix it.
And if this doesn't help you, then I would run the MS Word/Office installer and reinstall (or repair if that option is available) MS Word.
