do you want to replace the existing Normal.dotm? - How to fix this on mac?

 Go to this Path:

/Users/amoni/Library/Group Containers/UBF8T346G9.Office/User Content/Templates

Delete the Norma.dotm file. If word asks you to save it again do so and this error should disappear.
Free yourself from Normal.dotm pop-up once and for all

Credit : https://discussions.apple.com/thread/4906402