Add file to product

As I see in the creating product page, they have add file button at the right hand side. But when I add file, if doesn't show up in the product display page. I added a PDF file. I would like to know that by adding a file there, how would it show up in the product page.

It won't. That area enables you to add files which will be downloadable after purchase. If you want to add files to a product, you can just upload it via the joomla media manager and then add a link to it in the product description.