Word - 15 arguments

Question

I am using trying to use from my windows form. I have added a ref to the word.dll. Word.Document aDoc = WordApp.Documents.Open(ref fileName, ref missing,ref readOnly, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref isVisible,ref missing,ref missing,ref missing); This gives error that no method of open has 15 parameters. Where can I find out the parameters it is expecting and how many. I already use object missing = System.Reflection.Missing.Value; so I don't have to specify my argument values. Thanks