1. Make sure that all available software updates are installed on the Mac. (Important: Please back up your Mac before updating. ) Be sure to update the iPhone and iPad systems to the latest. (Important: Please back up the iPhone and iPad before updating the system. ) Try viewing PDF files with a book application on iPhone and iPad to see if the problem still exists. Check whether your friend's Mac and your Mac system version are exactly the same.
2. on iPhone and iPad, tap settings > general > restore > restore all settings. IPhone and iPad will restart, and all settings will be removed, but no data and media will be erased. On the Mac, try to create a new administrator account and log in with the newly created administrator account to see if the problem still exists. If possible, try reading the same PDF file on multiple devices with the same system version to see if the problem still exists.
3. Click and hold to open the file, choose to open the file with another application, and select the browser to browse.