I am sorry that the you've experienced slowness with the latest version (16.04.05) of Acrobat Reader for iOS.
Would you please provide more details about the problem so that we can investigate further?
Thank you for your help!
We just released Acrobat Reader for iPhone and iPad version 16.05.18 on May 6, 2016.
This update includes the fix for the file browser performance issue that you reported earlier.
Would you please give it a try and let us know if it works for you?