Currently, the only way to have a PDF spec link on a product detail page, a user must upload this to the File Cache in the CMS and then in the Product Manager add the HTML to create a link in the description to display it online. The product manager should allow for the upload of spec sheets against a product item and a download link should be made visible automatically on the site (this will also need styling in the standard templates).
We are planning functionality to allow for multiple images and files to be uploaded and configured for products in a much simpler and more flexible way. We will take this into consideration when we start planning that update.