This indicates an attack attempt to exploit an Out of Bound vulnerability in Microsoft Edge.
The vulnerability is due to an error when the vulnerable software attempts to handles maliciously crafted PDF file. An attacker can exploit this by tricking a user into opening a maliciously crafted PDF file and execute arbitrary code within the context of the application.
Windows 8.1 for 32-bit Systems
Windows 8.1 for x64-based Systems
Windows Server 2012
Windows Server 2012 R2
Windows RT 8.1
Windows 10 for 32-bit Systems
Windows 10 for x64-based Systems
Windows 10 Version 1511 for 32-bit Systems
Windows 10 Version 1511 for x64-based Systems
Windows Server 2012 (Server Core installation)
Windows Server 2012 R2 (Server Core installation)
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor