Present situation-
I restarted Mac in Safe Mode with no change in the issue.
I created a new User (admin level). Same issues with this User.
Turning off SIP (Mac's System Integrity Protection) with (Recovery Mode) Terminal then normal restart made no difference.
I have done a fresh install of Mac Mojave OS (after running Disk First Aid from Recovery Mode) and applied all updates.
I have done a complete removal of Office 2011 (following MS support articles, not just moving Office 2011 to trash).
I have done a complete removal of Office 2016 (per MS support article, inc manual removal of the com.microsoft.... files, etc.). Also removed all Office 2016 licensing.
Then did a fresh download and reinstall of Office 2016 from my Microsoft account (pkg 16.16.20030700).
My Mac User (Admin) has read/write permission to MacintoshHD. Word documents are all associated (Get info, Open with) to open with Word.
My current situation appears to be that Office does not recognize documents at the main/top level of my MacintoshHD (internal boot drive).
Word will neither save documents to nor open documents from MacintoshHD. Save attempt results in "Word cannot complete due to file permission error'. Attempts to open Word documents on MacintoshHD result in "Directory name isn't valid" error message. Word
WILL open and save to the desktop and documents within a folder.
At least I have regained that functionality.
Strange thing is, I have been using Office 2016 for over 3 years without this issue.
I am now wondering if office 16.16.20 created this issue vs. prior builds?