To reference a PDF in a URL to view a PDF without using the Scene7 viewer, use the following URL:
http://<domain>/is/content/<companyname>/<name of the pdf without extension>
For example, http://sample.scene7.com/is/content/CompanyName/pdfname
As PDF is not an image, but a static content, it's necessary to modify the URL as /is/content/ instead of /is/image/. Make sure that the PDF has been marked for publish or else the URL returns an error. It's necessary that the PDF is marked for publish after upload, to avoid delivery of all PDFs in the existing eCatalog/PDF workflow.
You can read more information regarding serving static content here: http://microsite.omniture.com/t2/help/en_US/s7/is_ir_api/index.html#Serving_Static_(Non-Image)_Content