My saving and opening problem with .docx format seems to have resolved itself.
Went searching in Microsoft's forum, read of similar issues, found a few tricks to try.
I closed Word, reopened it, went to preferences to ensure "Show Document Gallery when opening Word" was checked (it was).
I then opened several files in several different folders, all opened as per normal.


Probable cause was, under my breath I was mumbling about resorting to Apple's "Pages"... (I really can't abide by Pages, it's in the too hard basket)



Anyway, now much relieved !