This indicates an attack attempt to exploit a Security Bypass vulnerability in Adobe Acrobat and Reader.
The vulnerability is due to an error when the vulnerable software handles a maliciously crafted PDF file. A remote attacker can exploit this to bypass security mechanism on vulnerable systems.
Adobe Acrobat DC Continuous 2019.010.20100 and earlier version for Windows and macOS
Adobe Acrobat Reader DC Continuous 2019.010.20099 and earlier version for Windows and macOS
Acrobat 2017 Classic 2017 2017.011.30140 and earlier version for Windows and macOS
Acrobat Reader 2017 Classic 2017 2017.011.30138 and earlier version for Windows and macOS
Acrobat DC Classic 2015 2015.006.30495 and earlier versions for Windows and macOS
Acrobat Reader DC Classic 2015 2015.006.30493 and earlier versions for Windows and macOS
Security Bypass: Remote attackers can bypass security features of vulnerable systems.
Refer to the vendor's advisory for updates: