Training my dog to go potty inside as well as outside?

I have a two year old chi mix that I got from the pound a few weeks ago. She's already trained to go potty outside so that was an easy thing for her to adjust to. Since I'm gone during the day, I'd like her to be able to use puppy pads as well for inside. Is it possible for her to learn to go inside on a pad when she already knows how to go outside? How do I even do it?