Wrare Wright Wrant ...
This happens every couple of months.
Whilst working on a huge document, MS Word spontaneously decides to change to overtype mode, and without realising it, I start writing over stuff I wanted to keep. (I tend to type looking at the keyboard, so don't notice what's happening for ages sometimes.)
When I finally discover what's happening, I don't know how many Undos ago this started, and then have to go to Tools / Options / Edit, to disable Overtype mode, to get back to normal.
Very infuriating - probably some fly-by-night software producer ......
Yeah I know I should write to MS - I don't have the time to find out how!