As our "resident curmudgeon" stated, the best approach is to not convert from PDF.
The second best is to not expect the conversion results to be usable as is. Expect to need to use Calibre's Editor, or Sigil, to laboriously massage the ePub conversion output into a reasonable ePub and then convert that ePub into the final format desired if it is other than ePub.
See my response in post #4 in this thread:
https://www.mobileread.com/forums/sho...d.php?t=273001