Have you tried enabling "Screen Brightness Lock" for the Acrobat DC app?
For Acrobat DC for Android, the option is available in the app. Tap the action bar menu and select Settings > Screen Brightness Lock.
For Acrobat DC for iOS, the option is available in the iOS Settings screen. Go to Settings > Adobe Acrobat and select Screen Brightness Lock.
The option prevents the screen from dimming/turning off when Acrobat DC is running in the foreground, which in turn prevents your device from locking.
Hope this helps.
Thanks for answer..
As settings can be accessed only through menu.. I was trying to search settings in side bar so it was missed..
It would greatly help if same side bar have all the settings and help section and pressing menu also opens the same side bar.. this way it could be easier to access it
As an FYI for any iOS user of Acrobat DC (iPhone, iPad), there is also a Screen Brightness Lock on the iOS version as well. Go to Settings > scroll down to Acrobat DC at the bottom > Screen Brightness Lock.