Hello, thank you for reaching out to Microsoft Q&A.
Do you have any add-ins installed? Are you able to edit the documents normally in Safe mode?
Click Windows + R key, type winword /safe, and click Enter.
Please try to edit the documents normally.
If it works, disable third-party add-ins (File > Options > Add-ins > COM Add-ins > Delete)
If you're still having issues, repair Office applications.
Go to Start > Settings > Apps > Installed Apps > Locate Microsoft Office in the lists, click the three ellipses icon, and select Modify.
Select Online Repair.
Let me know if you still need more help.