Blio has two different formats for book files.
Fixed view books are PDF files that have been converted. Most of the time, fixed view books are children’s books or books with lots of images. The reason the files are fixed is to ensure that the layout matches the publisher’s original specification. These files do not support the adjustment of text in order to prevent images from showing up on different pages than the publisher intended. Zooming and Guided zoom are available for books that are fixed and have smaller fonts.
Flowed view books are EPUB based files and allow font adjustments. These types of books are usually novels. Flowed view books also allow for the changing of background colors and font changes. Because flowed view books are adjustable, they do not have static page numbers. As the font is adjusted, the number of pages in the book changes.