Digital copies are being used more and more on DVD and BluRay releases. They may cost a little bit more, but they are so worth it. After you transfer the movie's digital file into iTunes, you can easily make a copy to play on your Apple iPad. This video will demonstrate exactly how to transfer a digital copy movie to an iPad.
This example uses Star Trek (2009). Simple insert the DVD into your computers disc drive and find the digital copy of the movie. On a Mac, the file will show up as a DMG (Star_Trek.dmg). When opened, it will give you the movie application (Star Trek.app) which you will open— it automatically opens up iTunes, to the movie menu, where you need to input the redemption code that came along with your DVD. The movie downloads into iTunes, then you just need to update the video file to your iPad just like you would an iPod or iPhone.