When I insert a caption, for a table that was created in EXCEL, and copied into word (retaining the source formatting), the complete document becomes protected so that it can't be modified or edited.
1) Word tells me that the document has been protected
2) I am the only author
3) It does not allow me to remove the protection
4) This was not the first or only caption inserted into the document, other inserts appear not to have created no problems

I have recovered an earlier version, reinserted the table, and tried to insert a caption, and the problem recurred.
I have also had one previous instance of the problem, when adding captions to images in a different document

So, can any body explain:-
1) Why this occurs and how I can prevent it?
2) How to remove the protection from a document once they have been applied?

Word 36 + windows 10