Since Big Sur 11.2 on my iMac I have had trouble with my PDF apps. I have several because not one has all of the capabilities I need. The problem was after working with a PDF in any app other than the default, when I tried to reopen the PDF in the Default app it would crash/refuse to launch with the error message the I did not have permission to open that app. After about 18 hours of struggle, rebuilding Launch Services, resetting the SMC, reinstalling the system, deleting the caches, reinstalling the apps, nothing changed! Then I went into the General Preferences and turned off RECENT ITEMS and rebooted. The problem has not reappeared in the past 24 hours. This seems to have solved the problem. I am not a programmer and cannot explain why this works but it does. To be sure I reenabled the RECENT ITEMS and the problem reappeared. As you might imagine I promptly turned it off, rebooted and all is well again.