Editing the format of a Word document

Hi
I have a procedure in vb.net that create a word document. Here is my code

Code:

---

Dim wrd As Word.Application
Dim doc As Word.Document
Dim rng As Word.Range

Try
    wrd = New Word.Application
    wrd.Visible = False
Catch ex As Exception
    MsgBox("An error occured while printing, please try again")
End Try

doc = wrd.Documents.Add()
rng = doc.Range()

...

For Each StringDr In StringDv
            Select Case StringDr("No")
                Case 502 '1.2
                    rng.Text = rng.Text + StringDr("Message")
                Case 503 '1.2.1
                    rng.Text = rng.Text + StringDr("Message")
                Case 504 '1.2.2
                    rng.Text = rng.Text + StringDr("Message")
            End Select
Next
doc.SaveAs("c:\OperSeq.doc")
wrd.Quit()

---

Now What I would like to have is when I enter in the case 503, I would like that it put this "StringDr("Message")" text in bold in my word document.

Does somebody can help me with this?

Thanks in advance