Hmm, some assumptions are needed because of your wording:
You said: "I have recently purchased a CD from the iStore, using my iPad." First, I am guessing "iStore" means "iTunes Store". Second, the iTunes Store does not sell CDs, they sell music albums. So I am assuming that is what you mean.
If you're trying to get music that you purchased from the iTunes Store on your iPad moved to iTunes on your computer, then on your computer, open iTunes' Preferences (under the leftmost item in iTunes' menu bar), then choose the "Store" tab on top, and select the automatic download categories you would like to pick up from your iPad from now on.