Hello, epiphany, and welcome. I, too, have a Sony 500 and use it (some) for math and science - mostly PDFs. If the PDFs you have do not have DRM protection, then I recommend you try the free PDFLRF utility described here:
https://www.mobileread.com/forums/sho...ghlight=pdflrf
I use it all the time and works pretty well. If your PDFs are protected, there are currently no conversion utilities available although Sony is talking about supporting them in the future. Good luck!