There are tons of PDF to EPUB converters but almost no EPUB TO PDF.
Calibre supports the conversion of many input formats to many output formats. It can convert every input format in the following list, to every output format.
Input Formats: CBZ, CBR, CBC, CHM, DJVU, EPUB, FB2, HTML, HTMLZ, LIT, LRF, MOBI, ODT, PDF, PRC, PDB, PML, RB, RTF, SNB, TCR, TXT, TXTZ
Output Formats: EPUB, FB2, OEB, LIT, LRF, MOBI, HTMLZ, PDB, PML, RB, PDF, RTF, SNB, TCR, TXT, TXTZ
You can try Go4ePub.com.
According to my experience the results are slightly better than with Calibre.
I recommend to try this free online converter convertio.co , I have used it for a very long time without any problems ever!