Dear Jim,
I appreciate your desire to help, but as other people have said, there is a single problem that hundreds (and perhaps thousands) of Mac MS Word 2015 users are having that is identical, regardless of the cause. Whenever we try to open a Word document, we
get the message that we don't have permission to open the file.
However, News Flash!!
The problem, which has been happening on my computer for almost a year suddenly, today, stopped happening. I can now open all my word documents without a problem. I have no idea why it's fixed, but I sure am glad it is!!!