Document Index is a view for all folders and documents in Boardeaser. The advantages of using the document index are that you easily get an overall view of which documents are under which folders. It is convenient to use document indexes if you have an extensive collection of many folders and documents.
When you are inside Documents, click the button with a small arrow on it. Click on "Document Index".
This is the Document Index view. From here, you can open folders and documents in the same way as you do in the regular Document view.