I've seen this earlier but never got time to bother looking closely into the problem. So when I open a pdf file I created (long time ago, though in 2014). I see this error message from Preview:
But it's a lie, because of two things:
First, it's Get Info dialog:
Where one can clearly see the Permissions section, where it says Read & Write for peetonn (Me).
And who am I?
$ whoami peetonn
ls -Al@ output:
$ ls -l@ . total 19936 -rw-r--r--@ 1 peetonn staff 5.0M Dec 22 15:21 window.pdf com.apple.metadata:_kMDItemUserTags 42B com.apple.quarantine 22B
Could it be that these Apple's extended file attributes did something nasty? How do I fix that? Btw, if I hit Space for previewing the file, I can read it...