This indicates an attack attempt to exploit an Use After Free 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 XI (11.0.11) and earlier 11.x versions
Adobe Reader X (10.1.14) and earlier 10.x versions
Adobe Acrobat XI (11.0.11) and earlier 11.x versions
Adobe Acrobat X (10.1.14) and earlier 10.x versions
System Compromise: Remote attackers can gain control of vulnerable systems
Apply the most recent upgrade or patch from the vendor.