On the page where you want the file to appear, click on the "Edit" link at the top of the page. Scroll down to the "File attachments" section. Click on the "Browse" button and navigate to the file you wish to upload and select it. Then click on the "Attach" link. Your file will upload and will appear in the file list for the page you are on. Below the "Description" text box for you file, there will be a url that begins with "http:" You can copy this link and and use it in a "href" tag within the body of your page, like so:
<a href="http://pfoho.harvard.edu/%3Ca%20href%3D"http://THE">http://THE LINK YOU COPIED">the name of the file</a>
Note: a table with all the uploaded files for the page will appear at the bottom of the page, but this is only visible to users that are logged in, so you should put a link to your file, using an href tag, in the body of your page.