Hope you are doing well and sorry for the trouble. As described you get the error message: You do not have permission to open the application even though everyone has read and write permissions.
Is this a behavior with a particular PDF file or with all the PDFs that you try to open? Please try with a different file and check. Also, please share the screenshot of the error message for a better understanding.
If the file is saved on a shared network/drive please download and save it to your computer locally and then try to open it and check.
What is the version of the Adobe Acrobat/Reader DC you are using? To check the version goto Help > About Acrobat and make sure you have the latest version 21.01.20145 installed. Go to Help > Check for Updates and reboot the computer once.
If it still doesn't work, please repair the installation (Win Only) go to Help > Repair installation and check if that works.
If it still doesn't work, please create a new test user profile on Windows with full admin rights or enable the root account on Mac and try using the application there.