Click on the paragraph mark in the formatting toolbar to reveal non-printing formatting characters. That will include hidden text, which will be displayed with a dotted underline.
Nonprinting Formatting Marks by Suzanne Barnhill, MVP
This is a toggle. I usually work with these showing and then look at print preview to see what will print, or toggle the display off, and then back on.

When it is hidden, you can accidentally delete it, yes.


Also, if you truly want to be deleting this, look into Track Changes which lets you mark up documents as you prepare them, then accept all changes for the final document.