Documents can be uploaded in the same way as images. Read more about that here.
Placing documents in your theory page
In the toolbar, click the Insert button. Choose Link in the drop-down menu. A pop-up window will appear with some options. Paste the reference link in the field labeled Source or choose the correct file from the list labeled Link list.
You can furthermore change the link text to display in the theory page. You can change the icon using the drop-down menu labeled Class.
Using the drop-down menu labeled Target, you can change choose whether or not to have the (download) link open in a new window.