Cant save MS Word docs

Did you have an antivirus installed when you upgraded (3rd party AV)? If you did, it might have been the cause. It could be another program conflicting with it, based off what I saw in a search for this topic. If nothing works, try reinstalling Office, but with your AV program temporarily disabled.

Some programs have add-ins that load in office programs, sometimes AVs do it (but MS Defender/Security Essentials do not; also, MS Security Essentials shouldn't be used with Windows 10).

This being said, you could look and see if there are any extra add-ins that you can disable: How to remove Office 2013 add-in affecting program loading - Microsoft Community or Add or remove add-ins