The Kindle versions of David Allen's books are available from Amazon.com. A search for the books will show you the paperback, hardcover and Kindle versions if available in your country.

No, PDF is not a format that has been created by Penguin Group, the publisher of David Allen's books. Downloadable options include ePub(very common and compatible with iBook for iPhone, iTouch and iPad users,) Kindle (for the Amazon Kindle devices and readers) and Audiobook (spoken versions, as read by David Allen).