If your looking for something similar to the following, feel free to contact us at
quote@websitecm.com with specifics on what exactly you want, for a quote on what this would cost:
1) A "PDF Management" link in your admin menu, which transfers you to a PDF Management Page.
2) This page allows you to upload new PDFs via your Admin Section. (Would you want rename/edit/delete capabilities etc.?)
3) In your add/modify product page you have a drop-down menu listing "No PDF" and then the names of all the PDFs you've uploaded. If you select a PDF from the list the download link will appear on the Product Details page.