Had a customer who was having an issue adding a custom dictionary to the Microsoft Word. I found the following article that walked me through what to do.
Start by clicking File > Options > Proofing.
Add the custom dictionary.
We unchecked the RoamingCustom.dic. Clicked “Add”, and gave this new dictionary a name. Word asked if we were sure we wanted to add this new one. We clicked okay, and everything was working again.
I hope this helps someone else out there…