This indicates an attack attempt to exploit a 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.
Acrobat DC 2015.007.20033
Acrobat Reader DC 2015.007.20033
Acrobat DC 2015.006.30033
Acrobat Reader DC 2015.006.30033
Acrobat XI 11.0.11 and earlier versions
Acrobat X 10.1.14 and earlier versions
Reader XI 11.0.11 and earlier versions
Reader X 10.1.14 and earlier versions
System Compromise: Remote attackers can gain control of vulnerable systems
Apply the most recent upgrade or patch from the vendor.