A Little Background
The EPUB format, based on HTML/XHTML, is primarily used for the commercial book market. As the most widely used e-book format, it is supported by all major e-readers except Kindle (but that is about to change). The EPUB format is particularly well suited to mobile devices because it features reflowable text. This means that the text in an EPUB will reflow appropriately on a mobile device, no matter what its size. You can make the type larger or smaller, and the text will reflow appropriately. Text will not be cut off at the right margin, and you will not have to scroll horizontally to read the remainder of each line.
A Summary
Here’s a table that summarizes the differences between PDFs and EPUBs (as of 9/6/2011):
| Feature | EPUB | PDF (viewed with a PDF Reader) |
| Reflowable text | EPUBs automatically reflow (and hyphenate) and are well suited for mobile devices. | PDFs are written in concrete – remember, they’re based on printed pages, typically 8½ by 11, and (with many PDF readers) they do not reflow when enlarged. This can make PDFs difficult to read on smaller mobile devices. Note: Adobe Reader X and a few other readers give users the ability to reflow text; however, this feature is typically not automatic. |
| Change the font and specify a particular font size | EPUBs can do this. | PDFs cannot do this on many PDF readers. |
| Page turning | To turn the pages of an EPUB, users swipe horizontally. | To turn the pages of a PDF, users scroll vertically, and because of bottom page margins, there are typically larger gaps between pages. |
| Complex tables | With EPUBs, complex tables can be problematic, and content or coding often needs to be tweaked to make these types of tables work. | With PDF, although complex tables may not require tweaking, they are often difficult to read on smaller devices and pose problems (horizontal scrolling) when enlarged. |
| Graphics | On small mobile devices, graphics can be difficult to read in EPUBs. | On small mobile devices, graphics can be difficult to read in PDFs. |
| Search | Available with EPUBs. | Available with PDFs. |
| Annotation | Available with EPUBs. | Available with PDFs. |
| Copy text | Available with EPUBs. | Available with PDFs. |
| Audio and video | Available with EPUBs (depending on the e-reader). | Available with PDFs. |



