If Word cannot complete the save due to a file permission error, here are the solutions that have helped many fix the issue properly.

To resolve the 'Word cannot open the existing file (Normal.dotm)' error, reset the Normal.dotm file, use Open and Repair, and disable add-ins.

Repair My Word is a free utility that opens and fixes damaged or otherwise problematic Word files. Here are some of the common errors Repair My Word can overcome: "Word cannot open the document." ...