The usual advice for people who have to convert PDFs in a serious fashion is to use ABBYY Finereader. (The professional ebook producers who hang out here will swear by this product.)
This is assuming you need to OCR it to get a good conversion... but so so many PDFs do need exactly that. On account of they use images of the text,
sometimes with an OCR layer underneath but not a very good OCR usually.
Of course, depending on your PDF you may get lucky, and it will have clean text to convert to EPUB. You will still have to make sure to get the line unwrapping correct, and formatting will be mostly lost... that too is where professional OCR software comes in handy, since I believe it will detect and imitate far more of the layout.