[Peter T. Daniels]

It's possible that (somehow) your Backspace key has been assigned as
the Keyboard Shortcut for Select All.

You assign keyboard shortcuts to commands in the "customize QAT"
panel that you get from the tiny down-arrow at the far right of
the QAT.

Sadly, there doesn't seem to be a way to assign a keyboard shortcut
to Select All, so maybe just closing your document and quitting
Word is all you can do. Maybe even a Restart.

To assign keyboard shortcuts to commands and macros and such:

In the panel that opened up at the previous stop, near the bottom
left there's a menu that offers Assign Shortcuts. That's where
you can find any command you can assign a shortcut to. (It works
like assigning commands to letters and characters, which you do
in the Insert Character panel, which is the Omega icon Ω on the
Insert tab.)

On Friday, October 9, 2020 at 3:31:07 PM UTC-4, Eadavis wrote:
I'm typing a document in Word, and for whatever reason, when I hit my
backspace button, it automatically highlights all of the prior text, on
ALL of the pages. And of course, if you hit the Backspace button again,
it deletes everything. I'm about to have a heart attack, and need to
get this document completed for a grad school application. Someone,
please help!