Build 15014 for both PC and Mobile have been released to Fast Ring Windows 10 Insiders. A new e-book store is available, with Edge being the e-reader application. A lot of fixes and small additions this build!

After purchasing your e-books – you will find those in your Books library, which is a new hub entry in Microsoft Edge right next to your favorites, history, downloads and reading list. Windows Insiders in the US get to try out this experience today starting with this build and we expect to add more content over time.

Interactive reading experience: To navigate through an e-book, you can use the table of contents or seek bar at the bottom of the browser. You can search for words or phrases and ask Cortana to define specific words and view embedded video and audio content. And of course, pick up where you left of and leave bookmarks on the most interesting pages. You can even read your books when offline.
Learning tools: You can widen text spacing to improve reading fluency and benefit from typography tailored to reading efficiency.
Customize for you: Microsoft Edge is built for reading digital content on Windows 10 devices. You can make the reading experiences yours by changing the font and text size, themes, navigation control and more.
EPUB support: In addition to PDF files and books purchased via the Store – you can read any unprotected e-book in the EPUB file format with Microsoft Edge.