You should consider buying this book. The author spent a lot of time and worked hard to write and publish it. Why would you think you can download it for free when no bookstore would give you a paper copy? I don't believe any e-readers use PDF as its format is fixed so the text is not scalable to adapt to screen size.
The only way to read it is to put it on the e-book reader, but even so, there is no PDF editor to copy the text. The e-book reader is not a “portable e-book” (see also: this one) The author is not offering this e-book on pay-what-you-want. What I like is that you can buy this book for a 20.00 fee, and you can donate to his fundraiser for a kidney. Not exactly the highest, and still way to low in comparison to some prices of e-books for download. But it is a nice gesture. You don't need to sign up for his mailing list to be notified when it releases more books. This is not as useful as being a paying customer (or for getting the e-book through a friend).