Open your document on a "regular" PC (or MAC) using a "regular" Adobe Reader.
Then open the menu item "Document" -> "Security" -> "Show Security Properties" (and then, in the "Document Properties" window with the "Security" settings that will appear, you can also click "Show Details...", if you like -> note that "Booxtor" gave you the
screenshot of this window in German -> just click the
given web link).
Well, the real question now is ... exactly which setting(s) create(s) this problem (I don't know, sorry). I doubt the original author will agree to change all settings, but you might be able to convince him to change some of them, you just need to know precisely which of them should be changed.
The reply to this question might be of general interest ... sooner or later everyone will meet a pdf file which one will not be able to open, so it would be nice to have a "comprehensive" list of "harmful" pdf settings.