For installing Duokan, see here:
Duokan 2013 Installation
Also,see
https://www.mobileread.com/forums/showthread.php?t=209276 for KOReader, which has some PDF manipuation capabilities. It's not quite the same as true PDF reflow, as PDF doesn't understand paragraphs, but it should provide as good a guess as anything. It saves you having to reboot into a second OS.