Linking to a document is pretty easy. Just upload the PDF file to your site's server space - it might be an idea to create a site directory called 'documents'or something similar first.
Put the PDF into the folder, and then create a hyperlink to it wherever you want to on your site pages. The link can be an image, a button, or simply some text.
When some clicks on the link the document will download. Make sure you advise people that they're downloading a file - many people are very wary of doing this from sites they don't know.