This indicates an attack attempt against a Memory Corruption vulnerability in Foxit Reader or PhantomPDF.
The vulnerability is due to improper validation of ByteRange field when verifying the digital signature. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application.
Foxit Reader 18.104.22.1680
Foxit PhantomPDF 22.214.171.1240
System Compromise: Remote attackers could gain control of vulnerable system.
Apply the latest update from the vendor.