Secret documents

Secret documents, also known as secret docs, confidential docs or in some cases design specs, are a type of document that contains highly classified information, and as such are usually kept under close guard. These documents are usually packed in a manilla folder with a red "[Top Secret]" stamp on it, and contain information such as schedules for various locations, maps relating to a facility with updates on it, or even blueprints.

Soviet Union
During the Cold War, the CIA planned a mission where one of its agents would impersonate Major Raikov, infiltrate a Soviet base, and steal documents, but it was cancelled. In addition, documents detailing Metal Gear, as well as designs of the Shagohod with Granin's commentary were submitted to the CIA by Philosophers agent Ocelot shortly before Granin's arrest.

San Hieronymo Peninsula
During the San Hieronymo Takeover, the renegade FOX unit as well as former members of the Red Army kept guard of various classified documents in regards to its activities and locations of key establishments on the peninsula's Soviet missile base. A Soviet officer stationed at the Soviet patrol base was charged with guarding a trajectory printout of the ICBMG's launch coordinates as well as the date of the launch, although Naked Snake/Big Boss managed to steal it. Afterwards, spy units belonging to Big Boss's resistance movement managed to uncover locations of various classified documents in areas that they were stationed in, as well as submitting some of the classified documents themselves. Classified documents uncovered during the mission via the resistances spy units included a transportation route map that displays the locations of the town, the harbor, the rail bridge that connects the two halves of the peninsula, and the peninsula's main security base, as well as a supplement to the map that indicated a rotation schedule for Soviet soldiers manning a newly installed checkpoint; a map to the nuclear warhead storage facility, as well as outdated reports about the storage facility expecting a team to arrive to take the warheads; a map that gives the route and location to the guest house that was supplied to the rail bridge guards; a map that gave the location to the western wilderness high-security prison; blueprints of the missile silo, as well as blueprints for the ICBMG's booster rocket/Saturn V.

Costa Rica/Peace Sentinels
Design specs for various weapons systems and equipment were scattered around Costa Rica and Nicaragua. The Militaires Sans Frontieres procured several of these documents and developed their own variations of the weapons and equipment used, either by stealing them from the Peace Sentinels or by rescuing defecting researchers who supplied them with the documents for developing their own variations.

Behind the scenes
Secret docs were first introduced in Metal Gear Solid: Portable Ops as a gameplay element to proceed to the game, most of them being used to uncover new locations on the map, including the town, rail bridge, harbor, security base, warhead storage facility, western wilderness, and guest house. In addition, with the exception of the secret doc that was procured at the Soviet patrol base near the start of the game, the secret docs usually require a spy unit to find them before they can be unlocked. In-game coding and various hacks from Metal Gear Solid: Portable Ops indicated that the secret docs were intended to also be viewable in the equipment menu, but was removed from the final version. Similar to all plot-related items, they are represented as a red and black item box.

Secret docs reappeared in Metal Gear Solid: Portable Ops Plus, although this time, their usage and manner of being procured is completely different. The secret documents are procured by shaking up a random unconscious soldier or forcing a random held-up soldier to drop his belongings on the current map of the Infinity mission. Upon gaining it, it also reveals the location of the exit of the stage.

Secret docs, called "CNFDTL DOC" and "design specs," reappeared in Metal Gear Solid: Peace Walker, although this time they are utilized as a way to develop weapons systems. In some extra ops missions, one of the focuses is to procure design specs (which have five pages). These can also be awarded upon clearing a mission, or in some cases, clearing a mission with an S-rank. Although most of them pertain to weapons and equipment building for R&D, one dealt with cultivating Bananas. In addition, various unlockable items, more specifically the Rathalos wing, the Tigrex fang, the Gear REX mucous, the Gear REX concentrate, and the Gear REX super extract, operate under a similar manner to design specs that result in the creation of the Tanegashima, the Human Slingshot Post, and sling bands rank 1, 2, and 3, respectively. The sprite for the design specs/CNFDTL DOC is reused from the model viewer display of Huey's letter.