Secret File

A Secret Memo found in the Tropical Wilds.

Secret Files (also referred to as Secret Memos) are a type of Data Files found in Pikmin 3. Unlike most Data Files, these do not give any tips or information. Instead, they simply have a picture of some Pikmin with a random number from 0 to 9.

Shigeru Miyamoto stated in a Miiverse post that if a player collects all ten of these memos, the numbers they form, in order, will create a secret code. Once they are all collected, the player can then go to a Wii U exclusive website, http://www.nintendo.co.jp/pikpiksecret using the Wii U's Internet Browser, and enter their code to watch one of five secret video exploration logs. Each code is pre-written, and maps to a specific video. If the player wishes to see a different video, they must restart their save file from day 1 and obtain a different combination.

There are two Secret Memos per area. They are normally found in spots that are hard to find or access, but a few them can be found in relatively easy locations. They are always found in the same place, but the numbers in them depend on the code generated for that playthrough.

There is one video log that is not yet accessible via any Secret Memo code, and has not been officially released by Nintendo. It was found on Nintendo's website by analyzing the page's source code. It can be found on YouTube, and it features Louie.

Locations

Tropical Wilds

In a small pool in the area where the Calcified Crushblat can be found, between the islands with the Candypop Buds.
Beside the holed stump that leads to the Medusal Slurker with the Juicy Gaggle.

Garden of Hope

To do: Add a guide on how to reach the Elevator Platform one.
Care to do so?

On the larger set of Elevator Platforms.
In the overturned tin can that a Peckish Aristocrab hides in on the path to the Quaggled Mireclops.

Distant Tundra

On the snow wall next to the landing site. This memo is easily visible, and a leader can easily be thrown to the wall.
In the cave the leaders originally had to take to reach the Vehemoth Phosbat is a Bamboo Wall that requires Winged Pikmin to lift. In a structure in the center of the area is a Secret File. A Bulbear and Dwarf Bulbears are present in this area, so caution should be taken.

Twilight River

In the second river that is reached on the way to the Scornet Maestro is a stump with a Secret Memo on top of it. It originally has a pile of Fragments on it and requires a leader to be thrown over onto it.
On a ledge near the three Orange Bulborbs, accessed by throwing a captain off the vine path to the Scornet Maestro's tree.

Formidable Oak

In the Spotcaps behind the Reinforced Wall at the beginning of the cave.
In the area of the cave that must be lit up, a dirt mound is near a group of Candypop Buds towards the end of the cave. The Secret Memo is inside.

Exploration Log videos

The following are links to YouTube videos showing each of the Exploration Logs.