Acrobat DC Does Not Stay as Default PDF Handler

Hello,

      I work for a company that has upgraded from Acrobat and Reader XI to DC as of mid-2017. Ever since we upgraded to DC, our users cannot keep Acrobat DC (Standard or Professional) as the default PDF handler. We have computers running both Windows 7 and Windows 10, but the issue persists regardless. We are able to make changes through Default Program (associating the file type and protocols) and have tried the option under Preferences > General to "Make Acrobat the default PDF handler," but this only makes it so until the computer is rebooted or shut down.

      Since we cannot just keep all of our company's computers online without rebooting or shutting down, this obviously does not solve the problem. Is there some fix (whether it be in the registry in Windows or anywhere really) that can allow Acrobat DC (not Reader) to stay as the default PDF handler even after the computer reboots?

      It does not make any sense for the freeware version (Reader DC) to be the one resetting as default when the paid version (Acrobat Standard/Professional) is preferred for use, since it has all the extra tools available.

Thank you.