You can purchase genuine three-body e-books from official e-book stores or online reading platforms such as Amazon's Amazon Amazon Store, Google Play Books, and the Barney & Noble Nook Store. These platforms all provide legal e-book download and reading services. You only need to enter the correct e-book code to read it. In addition, you can also download unauthorized e-books from some third-party websites, but this may involve copyright issues. I suggest you use it with caution.