Directly behind the truck, right next to the main building.

This check is right next to the truck spawn, just up the stairs.

Directly inside the main building from the last check. In MPO+, this wall is broken, and just behind that is the location.

This is where the secret document is in the main game. The exit marker will be in the middle of the raised platform.

Second floor of the smaller building, in the control room.

The location here is just behind where the truck will be in the main game.