With Apple’s recent release of iBooks 2 and a new application called iBooks Author, extra attention is being given to the EPUB file format, a free and open e-book standard by International Digital Publishing Forum (IDPF).
As you would expect from a file format that has been designed from the ground up to be used for e-books, EPUBs primary claim to fame is that it is designed for reflowable content — so that no matter what display device it encounters (within reason), the content can be optimized on the fly to suit it.
So is EPUB a better file format for e-books than PDF?
The short answer is, probably, if your only concern is reflowable content, but not if you require some fidelity in your page layout and some extra bells and whistles.
The longer answer is more complicated.
Reflowable content is a bit of a pain point for PDF. While it has been technically possible to created a tagged PDF — which enables the automatic reflow of text and associated graphics to fit varying page sizes — for over 10 years, it has not solved the reflowable content problem.
This is largely due to the fact that the vast majority of PDF printer drivers and creators do not create tagged PDFs and tagging a PDF after it has been created is not an easy process.
Despite this PDF has become a contender for the e-book file format crown because of its device independence, fidelity, wide adoption, lack of big-time rivals and because up until a few years ago reading an e-book on a hand-held device — and not a desktop computer or laptop — was only something hardcore geeks did, which meant that there really was not a great demand for a file format solely focused on e-books. A general purpose PDF did a good enough job for a long time.
For PDF files reflowable content is an after-thought. Indeed, PDFs great claim to fame is that the content layout is fixed and identical on any device. So it is no surprise that EPUB does a better job at reflow than PDF.
But outside of content reflow EPUB lacks some essential features which many e-book users want and that PDF has had for years. Key features like linking internally or between EPUB files are missing and the text-centric nature of EPUB means that it is not suitable for publications where a precise layout is required.
Ironically as PDF has drifted from its original mission of a fixed layout format to offering more flexible layouts, EPUB will probably do the same, drifting from a flexible layout to a fixed layout as users and publishers demand it.
Is EPUB a better e-book format than PDF on the whole? No, not yet, but in 5 years once it has matured feature-wise, it might well be.