How do I add files to the risk plan?

In the risk plan page. On the left panel, click on the "Paper clip" icon.

On the upper is a green button. 

Click on it to see a menu of what kind of files you want to upload.

The type of files that can be uploaded are limited and mentioned in the pop-up.

You can also just drag a valid file to the drop zone (gray area) and it will be automatically added.