Protection is controlled by the Restrict Editing button/dialog.
This button can be found on both the Review tab and the Developer Tab.

I have uploaded a file with some screen shots of what I see when working with the corrupted file (after restarting the machine)

Most of the options in the ribbon are are unavailable, and when I attempt to inspect the document word tells me that I must change the permissions first

We need a Word file with the problem, not screenshots. (Screenshots may help, but not in the way the problem file would.)
Nothing is attached.
How to attach a screenshot or file in this forum.

I have attached a sample file that is protected - by inserting a caption

This was created using the same table of data from excel - which was copied into word, and I then inserted the caption (right click)

I created several test files, and got similar results each time.

In some case, the cells in the table appeared to be 'form fields' that could be edited, but in all cases the document became 'protected'. (It may be sensitive the formatting option chosen when copying the table?)

The problem has not recurred since the machine was restarted.

This sample file was created as a 'new document' - but the report that first exhibited the problem was created from old (office 2010) template.

My thoughts are:
1) The problem is 'in the table' copied from Excel?
But the previous occurrence in January involved images copied from google street view (did not involve excel)
2) The problems is a compatibility issue in an 'old template'?
Possible, but it does not occur in all documents, or when you start work, it seems to occur (sample of 2) when you have been working on a document for a while - and have copied and pasted a lot of stuff between files.
3) It's a 'machine resource' issue'?
Both instances have occurred when working with 'lots of data' - images and excel files, and the machine may have been running low on memory.
Shutting down programs and documents did not 'reset the machine' and once the problem has started it has a 100% failure rate.
RESTARTING the machine does appear to resolve the problem - untill next time???

Attached Files

Sample of Corrupted file.docx (18.6 KB, 9 views)