Can steam detect cracked DLC's?

I bought skyrim on steam a while back.... and after playing it... alot, ive gotten slightly bored and dont know what to do in it. So i was thinking of getting the DLC's. But then i came to the conclusion to, i dont have enough money right now... so i was wondering, if i were to pirate the DLC's if pirate bay and install them on my legit, bought version of Skryim, can Steam detect the dlc's? have you heard of it happening to anyone? and also, if steam does catch, what would happen. what would they do?? Any help would be appreciated! thanks!