This indicates an attack attempt to exploit a Memory Corruption vulnerability in Adobe Reader and Acrobat.
The vulnerability is due to an error when the vulnerable software handles a maliciously crafted PDF file. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted PDF file.
Adobe Reader 9.1.1 and earlier versions
Adobe Acrobat Standard, Pro, and Pro Extended 9.1.1 and earlier versions
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.