Ruy Lopez against Philidor Defense?

I really want to learn the Ruy Lopez opening for white, which will probably be quite time consuming, but my friend - who I would really like to beat - always plays the Philidor Defense (1. e4 e5 2. Nf3 d6).

So, my question is: Will a thorough study of the Ruy Lopez prepare me for beating my friend's Philidor Defense, or will it be a waste of time as soon as my friend plays 2...d6?

If a study of the Ruy Lopez can't be used for preparing for the Philidor Defense, which opening for white should I study instead? (I'd like to beat him in the Philidor Defense). Is it simply that I should study Philidor Defense for white? (I'm a beginner, and don't know much about openings, so my question might not make sense ...  if not, please educate me!)

If you want to beat the philidor, study the philidor. Studying the ruy lopez may give you some general understanding of kings pawn openings. But the theory is for ruy lopez only.

it doesnt take much study to cause problems for a philidor player. i suggest you play 3.d4 and 4.bc4 and learn all the traps white has in these lines. 

I don't think I'd ever call studying the Ruy Lopez "a waste of time" especially for a player starting out as it helps develop chess principles. But studying the Ruy Lopez specifically won't be directly applicable since he's likely to play c6 to push away the bishop. 

you don't study the Najdorf to beat Grand Prix Attack players... just study Philidor theory it shouldn't be that hard

If he plays the exchange philidor you could play Qxd4 then if Nc6... Bb5