We apologize for any inconvenience this issue has caused.
We have submitted an update that resolves the crashing problems introduced in 16.09.20 and we are awaiting approval from Apple.
We appreciate your patience.
Acrobat Reader 16.09.21 is available in the App Store now.
It should resolve the frequent crashes that you have experienced.
Please give it a try and let us know if it works for you.
We apologize for the inconvenience.