Re-download OS X iWork suite (Pages, Numbers, Keynote)
When you bought your Mac, you were prompted to "accept" the applications in the iWork suite, to be attached to your Apple ID for future download. 

If you did not do this, I suggest calling Apple Support or taking a trip to the Genius Bar. If you provide them your Mac's proof of purchase, they should be able to give you a redeem code for the App Store to download the suite. This will also link the apps to your Apple ID signed in on the Mac App Store for future download.