In addition, PDF has the concept of page numbers, (because it has rigidly defined structure/look) but AZW3 does not, as it's reflowable.
Unless Amazon generates you a sidecar .apnx file (this happens with purchased books), creating an index of arbitrary locations declared to be new pages.
You could try the
Kindle DX which has a bigger screen and is meant for reading PDFs. It will definitely work better than the PW(, though a tablet is still best). It costs $199.