The Freemasons wrote out a detailed plot to do so in the late 1800s in a document called the Alta Vendita
https://files.meetup.com/574112/Permanent_Instruction_of_the_Alta_Vendita.pdf
Multiple popes warned about it over the years... I think it was something like 5 popes in 20 documents.
Bella Dodd, a high ranking member of the Communist Party USA, testified that she personally had put some 1,100 communists into the Catholic Church's seminaries in the 1900s. She later converted to Catholicism and lamented of the grave harm she had done. She said they were working together and working their way up into positions of power in the hierarchy. They were also trying to become heads of the seminaries where they could do massive damage.
I spoke with an elderly priest a couple of weeks or so ago who had spoken to her some years ago. He confirmed that she said she had done this. Professor Alice von Hildebrand and her husband Dietrich von Hildebrand were friends of hers & also have confirmed this.
Here is a recent interview with Alice von Hildebrand discussing this topic:
https://www.churchmilitant.com/video/episode/intv-2016-01-27-e
Bella Dodd herself wrote a book detailing what she had done:
School of Darkness
https://www.amazon.com/School-Darkness-B-V-Dodd/dp/0815968043
A nurse in France details the plans they found in a briefcase of a man who died in the hospital after a serious accident. He had no identification papers on him so they opened his briefcase to see if they could identify him & contact his relatives. The briefcase was full of documents on how the Communists were infiltrating the Catholic Church. He was one of the seminarians, code named AA1025. That was for "Anti-Apostle - the 1,025th to enter".
AA-1025 Memoirs of the Communist Infiltration Into the Church
https://www.goodreads.com/book/show/1204310.AA_1025
(online copy:
https://archive.org/details/Aa-1025TheMemoirsOfAnAnti-apostle )
Dr. Taylor Marshall discusses the self-described "Sankt Gallen Mafia" in this video:
https://www.romancatholicman.com/what-is-the-st-gallen-mafia/
Cardinal Daneels, one of the power brokers who colluded with those of a like mind to elect Cardinal Bergolio (now Pope Francis) to the papacy, bragged about the success of the Sankt Gallen mafia (his term) in a biography, despite the fact that what they did was a grave violation of Canon Law.
See also Taylor Marshall's best seller, Infiltration: The Plot to Destroy the Church from Within
https://www.amazon.com/Infiltration-Plot-Destroy-Church-Within/dp/1622828461
Trojan Horse in the City of God: The Catholic Crisis Explained Hardcover – August 1, 1993
by Dietrich Von Hildebrand
https://www.amazon.com/Trojan-Horse-City-God-Explained/dp/0918477182
https://archive.org/details/trojanhorseincit00vonh
256: Infiltration: Pope Francis Rewound 150 Years – Alta Vendita and La Salette [Podcast]
https://taylormarshall.com/2019/05/256-infiltration-pope-francis-rewound-150-years-alta-vendita-la-salette-podcast.html