i have found another manual that is readable when you use a PTRS, it is next to the start.
1.) open the door that goes towards the flytrap
2.) then go to the window/barricade that is next to the fly trap
3.) lie down and looks for a small gap through the sandbags that are on the floor next to you.
4.) if done correctly, you will see a page of the field manual
Hope this helps

^