This indicates an attempt to exploit a buffer-overflow vulnerability in Adobe Acrobat and Reader.
The vulnerability is in the util.printf function and is caused by an error that occurs when the vulnerable software handles an invalid format string. It allows a remote attacker to execute arbitrary code via sending a crafted PDF file.
Adobe Acrobat and Reader 8.1.2
System Compromise: Remote attackers can gain control of vulnerable systems.
Upgrade to Adobe Acrobat and Reader version 8.1.3 or later.