Assuming you have a way to get to the response document, or you are already in the response document, try this:
Sub PlaceDocLinkInParent (rdoc As NotesDocument) REM "NOTE" rdoc is supposed to be the response document that you want the REM Doc Link for. As I said above, I will assume you have obtained this and REM just need to call this procedure to place the doc link.
Dim sess As New NotesSession Dim db As NotesDatabase Dim pdoc As NotesDocument Dim m_unid As String Dim rt As NotesRichTextItem Set db = sess.CurrentDatabase m_unid$ = rdoc.ParentDocumentUNID Set pdoc = db.GetDocumentByUNID(m_unid$) Set rt = New NotesRichTextItem(pdoc, "DocLinkField") Call rt.AppendDocLink(rdoc, "Link To Reponse Document") Call pdoc.Save(True, False) End Sub
Basically, this script gets the parent unid from the response, then gets the parent document with the GetDocumentByUNID method, creates a new rich text field in the parent and places a doc link in it.