Get the first document
You start on the roof of the building (M5,1). Get down on the street and kill the guard in front of you. Next, kill the second soldier behind the last building on the right. From here you can climb on the roof but it is better to enter through the door to the next building and go on the floor (M5,2).
There is another soldier there and, next to him, there is the document on the desk. On the table there is suppressed riffle ammo.
Take care of the officer and get the codes
Radio codes (side objective) are carried by the officer, he is in the building next to the opposite street (M5,3). The safest way to kill him is to get closer and use a knife so none of the soldiers is alarmed - in this case you must run to the east side behind the buildings and kill the Jager near the street, then, go behind the buildings from the north - the entrance to the building with the officer is in the back. After killing him carefully search his body to find the codes. They are useful in the later part of this mission...