Although sometimes it is possible to download an entire book depending on limits set by publishers, it may not be the best option for reading the book. Access to full downloads can be limited in duration, and a book no longer be accessible after a set number of days.
Downloading pages or chapter to PDF and using them in that form can be a better option. The PDF's can be highlighted and notated, and you have the option of printing them out.
Some books will allow a limited number of pages to be downloaded. However, this limit resets after 24 hours, so you can go in to the book again and download whatever the maximum allowance as often as you want.