Let me offer some suggestions for navigating scanned or photocopied pages in .pdf.
First, if you have either Adobe Acrobat Professional or Nitro PDF Professional you can process your .pdf to have hidden text. Hidden text allows the Onyx e-readers to see the text and to crop the pages effectively. Also, the e-reader can actually reflow the hidden text, but it will appear in the default selected typeface.
Second, if you can't process your .pdf to have hidden text, you could use the Selection Zoom or Zoom by Two Points features to select the area you want zoomed up to fill the screen. This feature should work in both portrait and landscape modes.