I would personally recommend Calibre, so you aren't limited to just ePub. However, keep in mind that PDF is designed to replicate the exact nature of a printed page, while ePub and other ebook formats (of which PDF is often incorrectly lumped) are designed so that they can "reflow". So if a word bumps against the border of the screen, it can be shifted to the next line.
Converting PDF to any other format often results in a less than optimal outcome.
In order to convert pdf to epub, we have to use the third party software called pdf to epub converter. Here we can try some free ones, such as calibre, zamzar, handbreak etc.
Of course, if you worry the free ones low quality, you can also try some paid tools.