如何在tcpdf上显示唯一值？

require_once('tcpdf/tcpdf.php');

$pdf = new TCPDF('P', 'mm', 'A4', true, 'UTF-8', false);

$pdf->SetCreator(PDF_CREATOR);
$pdf->SetAuthor('Your Name');
$pdf->SetTitle('Unique Value Example');
$pdf->SetMargins(10, 10, 10);
$pdf->SetFont('helvetica', '', 12);

$uniqueValue = uniqid();

$pdf->Cell(0, 10, 'Unique Value: ' . $uniqueValue, 0, 1);

$pdf->Output('unique_value_example.pdf', 'I');