Inserting Text into Word

Question

I have tried everything but I cannot figure this out. I need to insert text into an already open Word Document.
I am using C#.  This is an add-in, so Word is already open. If I use the new Document method like all the examples show it brings up fresh document and won't work (obviously) . What is the correct syntax for inserting text using C# if the document is already open. Thanks.