Open Document on IIS using C# ASP.NET MVC

I have asp.net mvc APP what open a word document and replace some tags.

I use COM Interop from Office. I know that openXML is the way, but i need to run with COM interop.

The code:

Document document = app.Documents.Open(@"D:\inetpub\temp\Prop_1.dotx"); //this returns null

When i run this code in a Console app it works but throw IIS not...

Any ideas?