Protected file missing

I had an Excel file that I routinely used and had protected it. Access was always done through the search feature so not sure exactly where it was kept. But since updating to High Sierra I can no longer find it! While trying to locate the file I came across some that have a red circle with a minus sign in the middle and when trying to open it am given this message: The folder “Documents” can’t be opened because you don’t have permission to see its contents.

This is MY computer and no one else has access to it so why am I getting this message and how do I regain access!