It is VoiceOver, a built-in feature in iOS.
It can be turned on by going to iOS home page -> Settings -> General -> Accessibility -> VoiceOver.
Be careful, though. Once you turn it on, you have to a different set of finger gestures to control iOS.
Please fix this problem. I am sure Adobe is committed to help people who have visual disabilities. I have poor eyesight. VoiceOver has helped me, and many others, significantly. Acrobat Reader has been working just fine with VoiceOver. Only the most recent version has this problem.
Thank you very much.
Please try to update Acrobat app. We have version released version 15.4 last week.