The PDF viewer on the PlayBook is pretty good but it is missing some ancilliary features that I wish RIM would add soon. Until then qPDF has stepped in by Qoppa Software. They have ported their Android apps to the PlayBook and their free qPDF Viewer is a solid back to the PlayBook PDF viewer. Sadly it still does not remember your last page but hopefully they will add that. qPDF also has a premium version called qPDF Notes ($9.99 in App World) that supposedly allows you to also edit PDF’s but I tried the free trial and it is very buggy.
Check out qPDF Viewer free in App World