fpdf with cakephp

I am using the library in fpdp's cakephp, I created a private method in my controller by putting together a basic pdf and then I called this method in an action but it does not generate the pdf ..

private method:

private function montaPDF(){
    require('fdpf/fpdf.php');
    $pdf = new FPDF();
    $pdf->AddPage();
    $pdf->SetFont('Arial','B',16);
    $pdf->Cell(40,10,'Hello World!');
    $pdf->Output();
}

and returns this error on my page:

  

% PDF-1.3 3 0 obj < > endobj 40 obj < > stream x 3R 2 35W ( r Q w3T04 30PISp Z * [ (hx + (j * d 7W endstream endobj 1 0 obj & lt ; > endobj 5 0 obj