How is possible for a 2MB pdf document to be blank ?

I'd go ahead and fire up that antivirus if I were you.

 

... and stay away from 2shared.com

Edit:
I don't really know if that site is all that bad. However it appears XPcentric is downloading some questionable files, from a security stand point.

 

You often find crackers put malware into those sorts of files. Usually they use windows and bind them together with 'IExpress' to make the malware execute at the same time as the pdf is opened. It is advised to give your system a quick scan incase they used blackshades (malware that runs on mac as well as windows).
In future open files with a text editor like vim or nano when you are in doubt (if it is a formatted document such as pdf or a document file). You can sometimes tell if there are unusual characters in it.

 

The message is written in invisible ink. Try pouring lemon juice on your screen.

 

Say what? It's a Mac.

Maybe that file is just corrupt. You could try it on a Windows system and see if anything shows up, just for kicks.

 

I can confirm the Blackshades Remote Administration Tools bin can not run on a mac.

-Eric the Ethical Hacker.