Word instance

I am trying to close from C# a documet that is already opened, but I don't know how I can access it (I have the name).

 I know that I can access the active word document like this:

Word._Application oWordApp;

......

Word._Document  oDoc = oWordApp.Documents.Application.ActiveDocument;

However, I need to access the document from it's name...

Can someone help me?

Tks.