Why do you want to convert the book to EPUB? If it;s to make it easier to read on a narrow screen you might want to consider this
k2pdfopt: optimizes PDFs for viewing on e-readers
I agree with thducks one gets the impression it will take some effort to convert - only the simplest of PDF's can be transformed to an EPUB without some, or a lot, of editing with an ePUB Editor.
BR