Word Automation on Custom Properties

Question

Hi,

I´m trying to make word automation on document custom properties(for a given 

property name change the value)

I put this code together:

Type Prop = Type.GetTypeFromProgID("Word.CustopParoperties");

 System.Object obj = Activator.CreateInstance(Prop);

Microsoft.Office.Interop.Word.CustomProperties CustomProp = obj as Microsoft.Office.Interop.Word.CustomProperties;

foreach (Microsoft.Office.Interop.Word.CustomProperty property in CustomProp)

            {   if (property.Name == valfind) property.Value = valreplace;   }

and I get this error

 Exception Details: System.ArgumentNullException: Value cannot be null.

Parameter name: type

 Source Error: 

 Line 53:             

Line 54:             Type Prop = Type.GetTypeFromProgID("Word.CustopParoperties");

Line 55:             System.Object obj = Activator.CreateInstance(Prop);

Line 56:             

Line 57:             Microsoft.Office.Interop.Word.CustomProperties CustomProp = obj as Microsoft.Office.Interop.Word.CustomProperties;

 As I understand I dont have the ProgID right

any ideas what should be there

I´m quite new to this and running out of hope

Thanks