Maybe it's the texts I tried. I have eBooks that are in PDF format (the one I tried is a Philosophy text), I have scans of texts, and PDF articles; plus I have a PDF of a scan that I clipped and made better (rotated properly, cut the black mark from the margin in the scan, split the double page scan into two pages, etc. - that's the best, of course, of all the PDFs I tried).
All of them displayed beautifully. The PDF viewer I'm currently using is Good Reader, but can't imagine it's the app I'm using.
It may very well be the app.