Official and Confidential: Official and Classified (公式かつ秘密?) is a file folder marked "O&C" containing extensively collected classified information on others. Against opponents who don't take precautions or fail a resistance check against the Noble Phantasm, they will have all extensive personal information including weaknesses and embarrassing information registered without any omission of fact. Against the Servants of Chaldea, it doesn't possess much of an effect due to them having little to hide. Even should they possess normally unspeakable secrets, they are already largely public knowledge through either the dissemination of their legends or modern textbooks, so they are useless as blackmail material.
Despite the Noble Phantasm being filled with extensive classified information, Assassin's Filing skill embodies how she can always instantly find the information she needs to due her method of organization being so methodical. Her Coercion skill allows her to utilize the information from the file as a "coercive binding spell" to blackmail opponents, tricking them into believing even a "silly secret" holds important meaning that forces them to yield to her authority. It is ultimately useless in the face of violence should the opponent decide to attack despite that.
Collected information on Gudako reads: "She's sold as a character who snaps at management, but actually they support her financially and she's just a servile pet who can't put even one toe out of line."