Hi Julie,
You should be able to create a Friendly URL for this using the URL Manager.
- Go to Administration > Advanced Tools > URL Manager
- Fill out the fields in the form, indicated in this screenshot:
- use data/sites/1/media/subfolder/filename.pdf
- use filename (note, you cannot use .pdf unless you have IIS configured to handle all files, not just ASP.net files)
- Click the "Add New Url Mapping" button next to the field marked '2' above.
Thanks,
Joe