Adding a document is a bit weird.
First, navigate to the "Documents" page in the sidebar
Next, click the plus symbol
Now enter any information about the document you think is relevant (summary, title, etc)
This next step is the weird one, but it's very important. Click on the "options" tab, and in the "excerpt" field type "Download", highlight it, and click the create hyperlink button
Now select the "file" tab, find the document you are uploading, select it.
Hit save and publish