Some encodings support alphanumeric values of any length. Others are limited to numeric values or to a specific set of characters. See the BarCodeType enumeration for details.
If you use characters that are invalid for the current encoding, the object will display a blank image.
RenderBarCode rbc = new RenderBarCode(); rbc.BarCodeType = BarCodeType.Code39; rbc.Text = "123456"; doc.Body.Children.Add(rbc);