Board Thread:Skyrim/@comment-125.60.240.214-20130115091923/@comment-60.231.52.25-20140315055358

you cannot steal essential NPC armour, if the essential id is removed from someone then yes you could.

however the greybeards robes are marked as non-playable, therefore even if you could get rid of the essential id you could not take the robes.

If you have played oblivion, think of the palace guard armour, you can kill the guards but not take their armour, this is because it is marked as non-playable.