Ah, thanks.
I use Linux Lite and it's pre installed PDF viewer, Evince.
Then I tried to open the PDFs directly in Chromium, and I got similar result.
Temporarly workaround : in local folder, I just renamed the file, adding "(chrome only)" so I remember that it works in Chrome/Chromium next time I need to have a look into it.
Also tried to print from chromium (to PDF file) in hope that the end result file would be readable in pdf viewer, but no - still the same visible result.