Let's leave "handles PDFs well" out of it for the moment.
Get an eink reader with a light (Paperwhite, Glow, etc) and also get a solar charger.
Since the charges last so long, even a small solar charger would be a workable solution. The built in light precludes the need for finding yet another power source for lights for use during darkness.
But for PDFs, depending on what you actually need of it, no small eink device does an outstanding job. Any efficient LCD tablet would do, but the bigger the screen, the more power it needs, so the shorter the charge will last , and the more time and current it's likely to demand from a charger, making a small portable solar charger inadequate.
On the whole, if power availability is the primary concern, go with small, efficient eink, and settle for the one that handles PDF least badly for your particular needs.
Last edited by ApK; 12-31-2012 at 11:26 AM.