Hmm, something of note that may or may not be the issue.
When I open the PDF using Chrome's built-in PDF viewer, there is some sort of interference that makes the first page, in particular, hard to read.
When I open the same PDF using Window 8's viewer, that interference is not visible. I haven't checked it using Adobe Acrobat or Acrobat Reader nor any of the viewers on my Ubuntu Linux box yet.
My initial thought is that WordPress didn't modify the file, but the original PDF has some layer that is rendering poorly in some viewers, which happen to include the Chrome viewer.
Can you try downloading the PDF and opening it up in a different viewer? Are you seeing the same results I am?