If Windows 10 keeps prompting you to associate an application to view PDF files when you double click to open them, try deleting the following registry keys and rebooting. This worked for me.
- Open regedit as an administrator
- Navigate to
Computer\HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.pdf
and delete the .pdf key - Navigate to
Computer\HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\FileAssociations\ProgIds
and delete theREG_DWORD
called_.pdf
- Reboot
This reset the default to Microsoft Edge and then allowed me to change the default to Adobe Reader.