Add description to PDF attachment

Using vb.net:

I can add a PDF as an attachment (importDataObject) to a PDF, and add a button that opens it.

I would like to add a description to the newly added DataObject.

The JavaScript reference goes along the lines of:

var mydataobject = this.getDataObject("AttachedPDF");

mydataobject.description = "What is the attachment";

translating this to vb.net:

     dim jso = pddoc.GetJSObject

     dim mydataobject = jso.getdataobject("AttachedPDF")

     mydataobject.description = "What is the attachment"

throws an error: "Public member 'description' on type '_ComObject' not found."

Can this be easily added?

Dave