Prevent apps from changing the default app to open PDF files? The Preview app used to be the default app to open PDF files. For some obscure reason, this is being changed into Photoshop every now and then.

If this happens, I do this:


Right click on a PDF file, Open With...
For some reason Preview isn't even in that list, so I click Other
Select Preview, check the 'Always Open With' box, and click Open
Then I right-click the file again, Get Info
The "Open With" part shows Preview, and I click the "Change All" button


And then it's OK for a while. But a few days later, without me changing any settings, for some reason PDF files are being opened with Photoshop again :(

Is there a way to prevent an app from binding file types to itself without my permission?

FYI I'm using macOS High Sierra 10.13.2 (17C88).
Try rebuilding your Launch Services database.

In Terminal:

/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -kill -r -domain local -domain system -domain user


Then reboot immediately.

References: 


https://www.tekrevue.com/tip/rebuild-launchservices-fix-duplicate-entries-os-xs-open-menu/
https://eclecticlight.co/2017/08/11/launch-services-database-problems-correcting-and-rebuilding/