PHP - FPDI is failing to open existing PDF

Question

FPDI is failing to load existing PDF. How to fix it?

require_once(APPLICATION_PATH . '/models/fpdf/fpdf.php');
require_once(APPLICATION_PATH . '/models/fpdi/fpdi.php');
$pdf = new FPDI();
$pageCount = $pdf->setSourceFile( APPLICATION_PATH . '/models/fpdi/en.pdf');
$tplIdx = $pdf->importPage(1, '/MediaBox');
$pdf->addPage();
$pdf->useTemplate($tplIdx, 10, 10, 90);
$pdf->Output(); 

Answer 1

 <?php
require_once('fpdf.php');
require_once('fpdi.php');

// initiate FPDI

$pdf = new FPDI();

// add a page

$pdf->AddPage();

// set the source file

$pdf->setSourceFile("PdfDocument.pdf");

// import page 1

$tplIdx = $pdf->importPage(1);

// use the imported page and place it at point 10,10 with a width of 100 mm

$pdf->useTemplate($tplIdx, 10, 10, 100);

// now write some text above the imported page

$pdf->SetFont('Helvetica');
$pdf->SetTextColor(255, 0, 0);
$pdf->SetXY(30, 30);
$pdf->Write(0, 'This is just a simple text');

$pdf->Output();