From a GPO Announcement (PDF):
The U.S. Government Printing Office (GPO) has made available for the first-time the official edition of the 9/11 Commission Report in an eBook format. The report details the circumstances surrounding the September 11, 2001, terrorist attacks, including preparedness for and the immediate response to the attacks, and provides recommendations designed to guard against future attacks. The book is available in print format at GPO’s retail and online bookstore. The entire report is also accessible through GPO’s Federal Digital System (FDsys), a one-stop site to authentic, published Government information.
The official eBook version of the report is available as an EPUB file and can be purchased for about $7.50 from BookU.com.
Read the Complete News Release from GPO