This indicates an attack attempt against an Information Disclosure vulnerability in Foxit Reader and PhantomPDF.
The vulnerability is due to an error in the application when handling a crafted PDF file. A remote attacker can exploit this to gain unauthorized access to sensitive information, via a crafted PDF file.
Foxit Software Foxit Reader 220.127.116.1126 and earlier
Foxit Software PhantomPDF 18.104.22.16826 and earlier
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor: