The first thing you need to do is to load your pdf file. You can do that through the Content Upload tab, found in Edit and Manage Website. Be sure to copy the URL for the loaded pdf file.
Next, you will need to make a navigation path to that pdf file. This can be done with a graphic (common for single pdf files) or with a hyper-linked list of documents (common for multiple pdf files). In the case of a graphic, you simply the image in Content Upload (which gets it up onto the web server) and then publish that image somewhere on your site, such as the hompeage or in a sidebar. After you place the graphic image on your site, simply link it to the pdf URL created in step one.