The third document
Go to the monastery's yard. The officer, that patrols a floor there, will have the safe codes. In that safe you can find the third document. The safe is in the building on the opposite side (M5,15).
Searching for Capo
Now it is time to eliminate the main target - Capo. Sadly, it won't be that easy - after you kill him, you must search his body. Capo can be found in the upper square (M5,17) or on the lower levels. He looks like an officer so you can easily identify him - the quest marker can points him as your target when you are close enough to him (about 15 meters). Try to identify him by using your binoculars when standing on the upper balcony. Look at the square.
If you want to complete this objective quietly then start from the southern side of the monastery. Go through the corridors, you can access them from the entrance in front of the belfry, and by doing that you can clear the upper square.
But if you are certain that the target is not in the upper square then, from the room with the safe, you should go down to the lower levels. It is possible that he is hiding there (M5,16).
The last document in the cave
The last, fourth document, is in the lowest level of the building, in the cave. The descent is in the north-west part of the building (M5,16). There, you can find 2-3 enemies.
At last, you can go to the evacuation point (M5,18). You can get there by passing through the "cleared" areas following your own path. But it is faster and safer to sneak from the north, from the road to the monastery. You only have to beware the tank that patrols the road. When it is out of your site, run behind the building near the evacuation point and throw a grenade behind the building to make the soldiers check out that place (or you can blow up a barrel, car...).