A PDF I sent students was unreadable by a friend trying to read the file on Adobe Acrobat Reader n a desktop PC. This felt like a repeat of a problem I experienced in 2019 with macOS Catalina. And I had thought a Catalina update had fixed the error.
This time, on the Big Sur 11.3 Beta, the problem surfaced after I had stitched two PDF files in macOS Preview. The resulting PDF was not completely readable by Acrobat on either a PC or Mac. Page 5 of the 7 page document produced this error message:
A solution had been suggested for this new problem on this Adobe forum last year for macOS Mojave – when viewing the combined file in Preview, choose File > “Export as PDF” to generate a “true” PDF file. I tried this and indeed Acrobat could read all the pages.
Looks like it accurate to say macOS Preview corrupts a stitched PDF – goodness! Good to know.
Otterman speaks... 