Go to "Video on-Demand" page.
Click "Edit video settings"
Click on "References".
You have two option to add your reference
Option 1 : Enter you reference link.
Option 2 : Upload PDF file.
Click "Add References" button.
Click "Save" button.
Now to see your references.
Click on your video to open player page.
In player page in section references you will find them.
When you select any one of them it will be opened in another tab.