[...]
Dim myWord As Microsoft.Office.Interop.Word.Application
Dim curDoc As Microsoft.Office.Interop.Word.Document
  Try
     myWord = CreateObject("Word.application")
     myWord.Visible = False
     curDoc = myWord.Documents.Open("C:\test.html")
     curDoc.SaveAs2("C:\test.rtf", WdSaveFormat.wdFormatRTF)
     curDoc.Close()
     myWord.Quit(WdSaveOptions.wdDoNotSaveChanges)
[...]