Secret File

A Secret Memo found in the Tropical Wilds.

Secret Files (also referred to as Secret Memos) are a variation 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 1-9.

Miyamoto stated in a Miiverse post that if you collect all 10 of these memos the numbers in them will comanate into a Secret Code. Once they are all collected, you can then go to a wii u exclusive website and enter your code to watch one of five secret video exploration logs.

There are 2 Secret Memos per area. They are always found in the same place, but the ones you find in these places are randomized to form one of five codes.

Locations

Tropical Wilds

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

Garden of Hope

A Secret Memo can be found near the Elevator Platforms puzzle.
Another can be found in the overturned tin can that a Peckish Aristocrab hides in on the path to the Quaggled Mireclops.

Distant Tundra

Throw a captain onto the snow wall next to the landing site. This Memo is easily visible.
In the cave you originally had to take to reach the Vehemoth Phosbat is a Bamboo Wall that requires Winged Pikmin to lift. In a structure in the area behind it is a Secret Memo. Be careful as a Bulbear and Dwarf Bulbears are present in this area.

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 you must light up, is a dirt mound near a group of Candypop Buds. Use Pikmin to dig out the Secret Memo.