This trophy is easily obtainable within the first mission of the game, the same mission in which you obtain the bow.
To simply pin an enemy to a wall, first you should hold select on your bow, and make sure you have the "Carbon Impact Tip" equip, and then press
until you pick the "Strong Draw Weight", making it possible to pin an enemy, then simply hold down the shoot button to pull your arrow back and fire at an enemy when there's a wall behind him.
You know when you've done it successfully as the game will make you press
to retrieve the Arrow from their body, rather than walking over it like before, meaning they've been pinned. Which retrieving arrows from the pinned enemies body will help you get the