For this you must get through the forest in mission 7 without being detected by human enemies. There is a dog at the beginning of the section that will always attack you, this does not negate the trophy / achievement. You can restart checkpoints if you get detected. If an enemy sees you that's okay as long as you don't alert the entire camp.
Here is a video guide with English commentary!
Here is a playlist of guides for this game!
https://www.youtube.com/playlist?list=PL-HeW6XkKdUKe25WzwEqI...