If you follow the news, you'll know that Windows 10 and 11 has defaulted Edge as its default PDF reader. And they took another step again later by making it difficult to set any other as default (by resetting it back to Edge after a restart).
Luckily for those who loves using legacy products, we can now make a script to run on startup to change this to your flavour of PDF Reader.
1. Download a tool here: https://kolbi.cz/SetUserFTA.zip
2. Create a Temp folder on C: Drive
3. Extract zip content into the newly created folder.
4. Create a batch file with the following entries:
cd\Temp\SetUserFTA
REM Next line is for making Acrobat 9 Pro as default
setuserfta .pdf AcroExch.Document
REM Next line is for making Acrobat X as default
REM setuserfta .pdf AcroExch.pdfxml
REM Next line is for making Acrobat 15 as default
REM setuserfta .pdf Acrobat.Document.2015
REM Remove the remarks accordingly
5. Save the batch file under C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup
Restart your computer to test.