The State Department volume on Guatemala has a section entitled "abbreviations and cryptonyms." The entry for PBHISTORY reads "Central Intelligence Agency project to gather and analyze documents from the Arbenz government in Guatemala that would incriminate Arbenz as a Communist."
The PBHISTORY project was a post-coup project, utilizing documents found in Guatemalan government offices, presumably to provide post-coup justification for the operation. This page of a State Dept. volume notes that "The PBHISTORY team reviewed more than 500,000 documents", but "the report admitted that very few Communist damaging documents had been found."
Nicholas Cullather, Operation PBSUCCESS. The United States and Guatemala, 1952-1954. https://archive.org/stream/GuatemalaCoup/Guat01#page/n89/mode/2up
(At page 91 of 200): In early July (1954, Frank Wisner) sent two officers, REDACTED and REDACTED, of the Counterintelligence Staff, to Guatemala City to do a 'snatch job on documents while the melon was freshly burst open'. He hoped to find papers to enable the Agency to trace Soviet connections throughout Latin America and identify 'people who can be controlled and exploited to further US policy'. In addition, he thought the captured papers would conclusively prove the Communist nature of the Arbenz regime. He named the project PBHISTORY."