Thank you for your replies, I've just seen your latest but haven't tried what you've just said but......

The document I've actually been working on may have been the "copy" because I've noticed that when I save any changes to other documents, at the bottom a little "box" appears where it says "Word is saving **********" (= the document name) and there's a short box where a Black line extends as it's saving.

When I save any changes to the document I've been asking about, it saves the changes, but no Black line extends, the wording is there but the box is empty.