Trying to open PDFs from write protected media (eg SD Card with write protection set) results in an error
"Adobe Acrobat Reader could not open <file>, file type is not supported or file is damaged"
(Translation from german message)

This error shows up most times, on some PCs and also sometimes on same system doesn't.
There is no reproduceable logic behind it .

Works normal once write protection is removed.

WIN10 64, Reader Version 2021.011.20039 64Bit