What pidgeon said, plus when you use the Send to Kindle app you have the option to select to which devices you would like to send the books/docs. They are automatically stored in the Cloud too. You have to have a Kindle device or app or the Cloud Viewer (name?) to view the books/docs. If by chance you do not have a Kindle device or app, you can install one on most devices.
Currently: Kindle Touch, iPhone 5, and iPad 3.