Dim app As New MSWord.Application
try
Dim doc = app.Documents.Open("d:\test.doc")
If doc.ProtectionType <> 3 Then
doc.Protect (Password:="123456", NoReset:=False, Type:=MsWord.WdProtectionType.wdAllowOnlyReading, UseIRM:=False, EnforceStyleLock:=False)
app.Documents.save
End If
app.Visible = True
catch ex As exception
msgbox(ex.message)
app.Quit
finally
End try