Visual Studio Tools for Office (VSTO) can be used to develop add-ins (and more) for an Office application. In combination with the SharePoint Client Object Model, it could be used to retrieve additional information from a SharePoint site were the file is located.
You always need to specify a site URL when using the SharePoint Client Object Model. This URL can be retrieved from the document information panel.
This location can easily be retrieved in your VSTO add-in or document template. To retrieve this value use the following code snippet.