Installing fpdf in Yii vendor

I am trying to work with fpdf class in yii. So I import the fpdf shared folder into the yii vendor folder, then tried to import into the view file like:

Yii::import('application.vendors.*');
require_once('fpdf/fpdf.php');

      

        
        
        
      

    

then just insert the class like this

class PDF extends FPDF
{
// Page header
function Header()
{
    // Logo
    $this->Image('logo.png',10,6,30);
    // Arial bold 15
    $this->SetFont('Arial','B',15);
    // Move to the right
    $this->Cell(80);
    // Title
    $this->Cell(30,10,'Title',1,0,'C');
    // Line break
    $this->Ln(20);
}

// Page footer
function Footer()
{
    // Position at 1.5 cm from bottom
    $this->SetY(-15);
    // Arial italic 8
    $this->SetFont('Arial','I',8);
    // Page number
    $this->Cell(0,10,'Page '.$this->PageNo().'/{nb}',0,0,'C');
}
}

// Instanciation of inherited class
$pdf = new PDF();
$pdf->AliasNbPages();
$pdf->AddPage();
$pdf->SetFont('Times','',12);
for($i=1;$i<=40;$i++)
    $pdf->Cell(0,10,'Printing line number '.$i,0,1);
$pdf->Output();
?>

      

        
        
        
      

    

But it ends up with an error: "This pdf may not display correctly. And if I try to download and view, then it says" HTML document type (text / html) is not supported. "I added" header ('Content-Type: application / pdf '); "in the view file without help.

can anyone help?