You can buy books from any bookstore that sells ePub format. First of all, you'll need to install Adobe Digital Editions software (ADE) on your PC, and "activate" both your PC and your Reader in ADE. Once you've done that, you can buy any ePub book from a bookstore; the bookstore will generally e-mail you a download link which will download the book to Adobe Digital Editions on your PC. Finally, use ADE to transfer the book to the Sony.
It's a lot easier than it sounds

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