You would just use the API to download the file, then open it in Windows (the file extension would let Windows know what to open in). In C#, you just use Process.Start(<filename>) to open a file in its related application.
If you also want to see the indexes, you would have to build an interface for that. As you access the Document object, that gets you the indexes, and then you can download the document itself via its download link.
Here is the general Platform SDK documentation now:
and here is the .NET example of downloading a file:
If you want to view a document without bringing DocuWare up in a browser yourself, you can use URL Integration.