Isn’t this self-evident yet? From the NCTE website:

PLEASE DO NOT SEND US THE ONLY MATERIAL IN EXISTENCE��ALWAYS KEEP A COPY FOR YOURSELF.

I’m laughing that they would still have to publish this guideline after all of the years that we have been using computers to do word processing. It would seem evident on the order of, for example, if you stop your car on a hill and want the car not to roll down the hill when you exit the vehicle, then you must engage the parking break. Yet, if it’s one thing I’ve learned over the years writing process documentation, what seems most elementary and common sensical must often be explicated. Still, makes for fun reading. Or, it could just be that I’m getting punchier than usual given the time.