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epub 2 and epub 3 are both much better formats than PDF if you really want to publish ebooks.

PDF is not reflowable and results in a crappy reading experience unless the device screen size is just right.

PDF is ultimately for paper when you care about how the content fits on each page. A reflowable format will have to at some point be rendered to pages if one is to go to paper, and I can't think of anything better than PDF for storing that rendering.

epub is basically many html files packaged together and indexed. So rendering for printing can be taken care of with the right media-querying CSS.

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