Hope you are doing well and sorry for the trouble. As described the application is freezing when you open the PDF file.
Is this a behavior with a particular PDF file or with all the PDFs? Please try to open a different PDF file and check. If the file is stored on a shared network/drive please try to download the file to your computer locally and try to open it and check.
What is the version of the Adobe Acrobat/Reader DC you are using? To check the version go to Help > About Acrobat and make sure you have the latest version 21.01.20142 installed. Go to Help > Check for Updates and reboot the computer once.
If you are on Windows OS, please try to repair the installation from the help menu and check . Help > Repair Installation
If it still doesn't work, please try to turn off the protected mode for testing (Windows OS) and see if that makes any difference. Go to Edit > Preferences > Enhanced Security > Uncheck 'Enable protected mode at startup' , Turn off the protected mod and uncheck Enhanced Security > Click OK and reboot the computer.
Note: Please turn on the security after testing to avoid any security risks.
You may also refer to the steps provided in the help pages listed below: