Working with a word processing document and you press the Del key, what happens?

Well, nothing happens because it is not a key that is given primitive command access to the software.

Primitive keys - the keys that directly can be input into the program

Now, if you have the text cursor highlighted and you press the del key, it will delete the text, but that happens when you press a key that is able to put a value on the screen.

It will erase everything you have written.