Hi,
I haven't tested but if you setup a new registry scan to scan the registry key :
"HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.pdf\UserChoice"
And a REGvalue of "ProgID" , this should give you a list of the default applications for opening PDF files for each User / Computer, below is the Lansweeper instructions for scanning Registry Keys
https://www.lansweeper.com/knowledgebase/report-based-on-registry-keys/
Cheers
A