Taking full control of the device, effectively jail-breaking the computer to run any ARM-compatible software, after that point is an exercise left to the user.
Instead of purchasing e-books through a single online store to read only on compatiblesoftware (i.e. books bought from the Kindle Store can only be read on Kindle apps), Google lets consumers buy books either from its store or any other online vendor that sells books in EPUB and PDF formats, and read them on any device with a web browser.