Hard to guess how to close 'presentation mode'

First of all thanks for the great update!

My problem is the way how closing the presentation mode is done. I was trying tapping, long pressing, bottom edge swipe but non of those worked. I asked around and Andrew Hayzen told me I should double tap. It worked!
The issue here is that gesture is almost never used in other apps I have installed. Actually I can think only about two places where I double tap: Browser to zoom and circle on the lock screen.

Possible solution could be adding info about the gesture after a user went into presentation mode or, maybe even better, doing what gallery app does (as suggested by Andrew) and use just single tap to show the header.

SOLUTION: As discussed with James, DocViewer should use a single tap gesture for showing/hiding the header.