A new piece of malware, which uses PDF files to download a Trojan Horse, has been identified.

Symantec Security Response recently came into possession of an Adobe Acrobat PDF file that is exploiting a vulnerability and, when opening, drops and executes a malicious binary onto a user’s system.
The malicious PDF files are detected as Trojan.Pidief.G and the dropped files as Trojan Horse, according to a statement from the company.
The vulnerability hasn't been seen in the wild before and affects Adobe Flash. Once the unsuspecting user visits the web site or opens the PDF, this exploit will allow further malware to be dropped on the victim’s machine and possibly open a back door.