A family of Microsoft word processing software products for creating web, email, and print documents.
Thank you for testing that. Since new Word documents can be created and saved normally, Word itself appears to be working correctly.
Thank you for sharing the exact error message you're encountering. These symptoms can occur when a document was originally created by another user, transferred from another computer, downloaded from the internet, or has inherited permissions that prevent Word from modifying the file properly.
Were these documents originally created on this Mac using your account, or were they received from someone else or copied from another device?
In the meantime, as a workaround, try opening one of the affected documents, copying all of the content, pasting it into a new blank Word document, and then saving the new document to your Desktop. Let me know if you can edit and save that new file normally.