mouse no longer highlights text in Microsoft Word for Mac

The other Mac thing I'd suggest trying before talking to Microsoft is an SMC reset. MS will probably ask if you have done that. It is, admittedly, a long shot in this case but it checks off one more "tried that" box.

How to reset the System Management Controller (SMC) on your Mac - Apple Support

Try Microsoft's Office forums before trying their support staff.

MS made their forums less user-friendly than before by making it harder to limit answers to Mac subjects, but it can be done when you know the trick.

Start here: 

Results in Office - Microsoft Community.

That will display this page header:

1) Use the “Office Topic” pull-down to select your Office app, Word in your case..

2) Limit answers to Mac topics with the “Office Sub-topic” pull-down.

3) If needed, use the “Show Filters” option to further narrow the results.

Everyone there is both an Office user and a Mac user, something you can't say about Apple's forums. I believe you will find the contributors there knowledgeable and very helpful.

What version of Mac OS , what version of Office for Mac,what troubleshooting have you attempted?

I think you would benefit if you read the following and then re-post your question.

Writing an effective Apple Support Question

No worries. By the way, when answering a question, please click Reply in the box you replying to, it looks like you are speaking to your self. It's okay a lot of newbies do that.

Try restarting your computer in Safe Mode per the directions in Use safe mode to isolate issues with your Mac - Apple Support and then restart normally and re-test. If that does not work, please let us know.