This is a situation where it is important that both the Windows and Mac versions of Office are fully up to date.
On your Mac, go to the Word menu and choose About Word. You should have version 16.16
If you have any other version, install updates:
INSTALL UPDATES:
I think the first troubleshooting step to take is:
Ensure your Mac and Office have the latest updates. Here’s how to install updates:
Make sure your Mac has a working internet connection, then:
- Update Mac OS X. Open the App store and click on the Updates button. Install the updates.
- After, in any Office application go to the Help menu and choose Check for Updates to launch the AutoUpdate app.
Let AutoUpdate install updates and then restart your Mac.
If you use Antidote, Webex, Silverlight, EndNote, Zotero or other add-ins there is a potential for crashes unless you also update your add-ins to the latest update. Install updates for these programs if you have them.
On the PC, the version information is in different places and how to update instructions vary. Please ask how to get the latest update for Word for PC in a Word for Windows forum.