Data to be copied from Document Library TO Custom List

I want to design a Visual Studio application that can copy data from a  Document Library and paste it into a Custom List. There is a Document Library with a Content Type. We want users to click a button on the SharePoint 2010 site and that will  populate a custom List with same data as document library. So I can deploy a web part.

Both Document Library and List exist and have same columns. But the VS program has to populate the List with data in Document Library. Some validation will be required such as don't put duplicate data into the list.

Any sample code will help. Can this only be done via Visual Studio?

Thanks a bunch!!!

Mayank