Nook reads most PDF's comfortably. However, with really troublesome PDF's try soPDF (
https://www.mobileread.com/forums/showthread.php?t=32066) there is also a Windows GUI available (
https://www.mobileread.com/forums/showthread.php?t=67739).
It crops out white space and cuts each page into two, this fixes most PDF's where the font is too small to read even with reflow.
Two drawbacks, you lose all your bookmarks once you convert with soPDF, although you can add them later, and it overlaps each page in case text was cut off mid-line, although this is a setting which you can play around with. Good luck.