You can use k2pdfopt to adjust your pdf as you would like, beforehand, for any e-reader.
video -GUI introduction
http://www.willus.com/k2pdfopt/help/...t_wingui1.webm
e.g. see from 6:50 min. reflow mode + higher dpi for bigger letters (for any A4 pdf)
or use native mode(no reflow) + landscape mode for any A5 or similar size pdf format, that will be easily readable on 6" screen in landscape mode with margins cropped.
http://www.willus.com/k2pdfopt/