Am just saying what I have come across on the web, so don blame me if its not right. I just want to help :

In some cases, there are PDF files, which have imperatives links on the last pages. For example, you can take the footnotes. By what I know of PageRank, it is highly unlikely that the transfer of PR is going to be influenced by what is the particular page where the link is appearing. What i believe from this finding is that the entire PDF file is your 'URL', which is the only thing that accrues PR.