code: func RegisterPdf417(pdf barcodePdf, code string, columns int, securityLevel int) string {
  	bcode := pdf417.Encode(code, columns, securityLevel)
  	return registerBarcode(pdf, bcode, nil)
  }
docs: // RegisterPdf417 registers a barcode of type Pdf417 to the PDF, but not to the
  // page. code is the string to be encoded. columns specifies the number of
  // barcode columns; this should be a value between 1 and 30 inclusive.
  // securityLevel specifies an error correction level between zero and 8
  // inclusive. Barcodes for use with FedEx must set columns to 10 and
  // securityLevel to 5. Use Barcode() with the return value to put the barcode
  // on the page.