PDF attachments sent from eFax open as a blank document on iPhone

I receive faxes from eFax to my email on a regular basis - I click the attachment, it downloads, displays normally as a PDF, I click it to open - I see a blank document instead of the fax. the pdfs open normally on my computer.

The iphone 3g seems to be opening other pdfs w/o a problem, but not PDF faxes from eFax. Any ideas on what would cause this? or any other ways to open these PDFs?