How to generate PDF file using PHP ?

<?php
  
ob_end_clean();
require('fpdf/fpdf.php');

// Instantiate and use the FPDF class 
$pdf = new FPDF();

//Add a new page
$pdf->AddPage();

// Set the font for the text
$pdf->SetFont('Arial', 'B', 18);

// Prints a cell with given text 
$pdf->Cell(60,20,'Hello GeeksforGeeks!');

// return the generated output
$pdf->Output();

?>

<?php

require('fpdf/fpdf.php');

class PDF extends FPDF {

    // Page header
    function Header() {
        
        // Add logo to page
        $this->Image('gfg1.png',10,8,33);
        
        // Set font family to Arial bold 
        $this->SetFont('Arial','B',20);
        
        // Move to the right
        $this->Cell(80);
        
        // Header
        $this->Cell(50,10,'Heading',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');
    }
}

// Instantiation of FPDF class
$pdf = new PDF();

// Define alias for number of pages
$pdf->AliasNbPages();
$pdf->AddPage();
$pdf->SetFont('Times','',14);

for($i = 1; $i <= 30; $i++)
    $pdf->Cell(0, 10, 'line number ' 
            . $i, 0, 1);
$pdf->Output();

?>