Troj_Pidief.AR Trojan is the Trend Micro detection for an exploit code that takes advantage of a known vulnerability in Adobe Reader 8.1.1 and various versions of Adobe Acrobat. Learn more about the said vulnerability, identified as APSB08-13, in the Adobe Web site.

Upon successful exploitation, it connects to a IP address to download a possibly malicious file. As a result, routines of the downloaded file may be exhibited on the affected system.

Technical details can be found at this Trend Micro page.