This indicates an attack attempt against a Code Execution 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 X (10.0) for Windows and Macintosh
Adobe Reader 9.4.1 and earlier versions for Windows, Macintosh and UNIX
Adobe Acrobat X (10.0) and earlier versions for Windows and Macintosh
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.