There is no use of PDF or other e-Book formats. An example is "Oliver Twist". In practice you need a smart phone with larger screen and a keyboard to make this practical. One limitation is that there are very few free books currently available. Most of the searches I conducted for free books only found historical documents hundreds of years old. Another limitation is that older documents appear to be in the form of page images, rather than real text. This will result in them taking longer to download and be harder to read on a small screen. These are limitations which other e-books have as well.