Hope you are doing well and sorry for the trouble. As described you are unable to highlight the text in the PDF
- Is this a behavior with a particular PDF file or with all the PDFs? Please try with a different PDF file and check.
- What is the version of the Acrobat Reader Mobile application you are using? To check the version tap on the profile icon on the top right corner and go to About Adobe Acrobat and try to update the application from the Play store (Android) or App Store (iOS) and reboot the device once.