As long as you are looking to play music while offline, pinning the music works great. I don't know that it downloads it in a format that you can then manipulate (move to another device, etc).
you still can download it as mp3 using PC/Mac application or from web(web has download limit)
Oh Yeah, I agree. I was just trying to be helpful to OPCorrect, but I don't believe you can use a file manager to find the music on the N7 to retrieve the mp3, you have to use the downloader on a PC/Mac.
I should also note that you can't "buy a music cd from the play store". You buy an album, but it doesn't come as a CD, being the physical storage medium. If you buy an album from the Google Play store, and you want a CD, you have to download & burn it yourself.