The easiest way to backup Keynote on your iPad is to sign in to your Managed Apple ID account and make sure Keynote is turned ON (Step 5 below). This will sync all of your Keynote projects to the Cloud and will make them accessible on all future devices.
If you would rather backup your Keynote presentations in the Files app, scroll down to the instructions at the bottom of the page.
As an alternative, you can backup your Keynote projects to the Files app by following the steps below: