1. Open the Start Menu and Select Settings.



  2. Type "default" in the search bar and Select "Choose a default app for each type of file".



  3. Scroll down to find .pdf and click the App listed if it's not Adobe Acrobat Reader.



  4. Select Adobe Acrobat Reader from the list of apps.



  5. Adobe Acrobat Reader is now listed as the default app for .pdf files.