Is this an issue with a particular PDF file or with all the PDFs? Please try with a different PDF file and check. If the file is stored on a shared network/drive, please download it to your computer locally and then try again.
What is the version of the Acrobat DC and the OS you are using? To check the version of the application go to help > About Acrobat and make sure you have the recent version installed. Go to Help > Check for updates and reboot the computer once.
Also try to repair the installation from the help menu (Win only) and reboot the computer.