Illustration by Will Joel / The Verge Amazon's Kindle is a useful reading tool, especially if you tend to purchase your books through Amazon. If you have ebooks that you've purchased elsewhere, however — or have picked up off a free service such as Project Gutenberg — you need to be able to put it on your Kindle (or Kindle app). Getting a non-Amazon book onto a Kindle used to be a somewhat awkward process, involving attaching it to an email and sending it to your individual Kindle email address. However, Amazon's Send to Kindle service has improved vastly since then, and it ...