most of the time this happens with Word, it is because the document has been emailed to the NVDA user. Regardless of whether the NVDA user has opened it directly from the email or has saved it to their computer first and then opened it, Word will open it in protected mode, which is read-only and therefore it can't be edited and many of the ribbon options, like chnaging font or changing the view to draft view will not work.
To prevent that happening, press ALT+f to open the file menu, press the down arrow key three times to get to the Info menu, press Tab to enter that menu and then press the down arrow to get to the Protected View menu. Press Tab again and you'll be on the Enable Editing option and, if you press enter, that document will become unprotected and the NVDA user should no longer hear the warning that the document is protected and can't be edited. It will remain unprotected even after you close the document or shut down the computer. The same works with Excel files :)
I hope that helps.