This indicates an attack attempt to exploit a Denial-Of-Service 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 crash vulnerable systems, via a crafted PDF file.
Acrobat XI 11.0.11 and earlier versions Windows and Macintosh
Acrobat X 10.1.14 and earlier versions Windows and Macintosh
Reader XI 11.0.11 and earlier versions Windows and Macintosh
Reader X 10.1.14 and earlier versions Windows and Macintosh
Denial of Service: Remote attackers can crash vulnerable systems.
Refer to the vendor's advisory for updates: