What if I have an HTML file and not a PDF, can't it be turned into a book? Why? We would need the display not to work exclusively on *PDFs and images, but I need to display HTML files as books to customers. Is it going to be set somewhere, say in a plugin? ... do you offer such a service/product? Thank you very much for the answers.
Just chose HTMLs files for Source in the book editor. Then insert your files at Pages tab.