Ive tried a few converters including Calibre. I would question whether anyone who claims Calibre or similar software does a good job has actually ever used Calibre for this purpose. Ive found the converted files generally contain gibberish and have messed up layouts and graphics. The converters are especially bad at converting mathematical symbols and equations. For these reasons the converted files are unusable and the conversion software is essentially useless. I haven tried every conversion program on the planet. Someone with more patience than me can do that. However the only rmendation I would take seriously would need to state something like the following Useless software like Calibre does a terrible job at converting PDF to ePub; howeverpared to useless software like Calibre software XXX does a surprisingly good job