An ebook can be a fixed page that looks the same everywhere, or flowing text that adapts to any screen. That is the real difference between PDF and EPUB, and it decides which one you want.
PDF: fixed pages
A PDF records exactly where every letter, line and picture sits on a page of a set size. It prints perfectly and looks identical on every device. On a phone, though, an A4 page has to be zoomed and scrolled sideways to read. PDF is right for forms, papers with equations, illustrated books, and anything you will print.
EPUB: text that reflows
EPUB is essentially a small website in a ZIP file: chapters in HTML, a stylesheet, images and a table of contents. Reading apps reflow the text to fit the screen and let you change the font size, typeface, margins and background colour. It is the standard format for novels and text-heavy books, maintained by the W3C.
What about Kindle and MOBI?
Kindle devices historically used Amazon’s MOBI and AZW formats. Amazon’s Send to Kindle service now accepts EPUB and converts it for you, and no longer accepts MOBI. So for most people, EPUB is also the format to use for a Kindle. Kindles can display PDFs directly, but small screens make them hard to read.
Converting between them
- EPUB to PDF works well. You choose a page size and the reflowing text is laid out onto pages, ready to print. Try EPUB to PDF.
- PDF to EPUB is harder. A PDF knows where letters are, not which lines form a paragraph or which text is a heading. Simple, single-column books convert well; multi-column layouts, footnotes and tables may need tidying. Scanned PDFs need OCR first.
- Word to EPUB is the cleanest way to publish your own writing: headings become chapters. See DOCX to EPUB.
Comics are different
Comic books are usually CBZ or CBR: archives of page images. They don’t reflow, so for tablets and Kindles a PDF or a fixed-layout EPUB keeps each page whole. CBZ to EPUB builds one page per image.
Sources: W3C EPUB 3.3; Amazon, Send to Kindle supported formats.