Right after you get to the upper level of the mine, over the collapsed lift and the nearby ice wall.
A bit after you find the first Document, after you enter the part where you find ancient ruins. The Document is at the skeleton on the ground, to the left of the corridor.
In the big room, where you craft smoke grenades for the first time, during the main storyline. The recess on the left. The Document is on the table.
At the back of the biggest chamber, in the mine at the destroyed cannon with the rope aimed at the gate at the other side.
After you pass through the chamber with murals on walls and jump over onto three successive columns, you walk into a small corridor. Halfway through the corridor, on the ledge to the left, you find a recess and the Document inside.