A family of Microsoft word processing software products for creating web, email, and print documents.
The most likely causes can be fixed by either/both of the following:
- Restart your Mac... That chases away many gremlins like this, &
- Make sure that both your release of macOS & Office are fully updated
If you need further assistance please cite the specific versions of both macOS & Office in your reply. Include any additional facts you can supply such as any changes made on your Mac just prior to the onset of issue & whether you have any add-ins installed.