Before:
Type this word


After: Type tis word

When I try to change or retype something, what was previously there, disappears.

This has happened many times in past with Word but I can never remember the fix.

Does someone know it?

Sounds like the Insert key has been pressed. Typing will replace text as the cursor moves forward. Press the Insert key again and see whether it reverts to inserting text where the cursor is and pushing the existing text to the right.

Thanks,
That worked but I don’t understand it.
It doesn’t look like the insert key was stuck……….but not sure.
Is there a permanent way to keep this from happening?

The Insert key provides a toggle setting between Insert and Overtype modes. It wasn't 'stuck'. It was in Overtype mode.

__________________
Graham Mayor - MS MVP (Word) (2002-2019)
Visit my web site for more programming tips and ready made processes www.gmayor.com

It doesn't get stuck (or shouldn't). It toggles on and off.

So, if I understand, holding it down, or not, while typing determines the mode………..right?

No, just pressing the key once toggles it on or off. You don't have to hold it down while you type.

I went to take a look so I could mention showing the Insert/Overwrite setting in the status bar … and remembered that "Use the Insert key to control overtype mode" is now a preference. (plus a subsidiary checkbox for anyone who wants to use overtype by default)

Back at the original thought, right-click on the status bar and select (check) Overtype to get an Insert/Overwrite indicator in the status bar.

Thanks,
I don’t know why I’d ever want it but good to understand if it happens again.