How to create an Invoice with watermark FPDF

<?php
/*call the FPDF library*/
require('rotation.php');
class PDF extends PDF_Rotate
{
	function Header()
	{
		/* Put the watermark */
		$this->SetFont('Arial','B',50);
		$this->SetTextColor(255,192,203);
		$this->RotatedText(35,190,'Students Tutorial Invoice',45);
	}

	function RotatedText($x, $y, $txt, $angle)
	{
		/* Text rotated around its origin */
		$this->Rotate($angle,$x,$y);
		$this->Text($x,$y,$txt);
		$this->Rotate(0);
	}
}
	
$pdf=new PDF('P','mm','A4');
$pdf->AddPage();
/*output the result*/
$pdf->SetFont('Arial','B',20);
$pdf->Cell(71 ,10,'',0,0);
$pdf->Cell(59 ,5,'Invoice',0,0);
$pdf->Cell(59 ,10,'',0,1);

$pdf->SetFont('Arial','B',15);
$pdf->Cell(71 ,5,'WET',0,0);
$pdf->Cell(59 ,5,'',0,0);
$pdf->Cell(59 ,5,'Details',0,1);
/*set font to arial, regular, 12pt*/
$pdf->SetFont('Arial','',10);
$pdf->Cell(130 ,5,'Near DAV',0,0);
$pdf->Cell(25 ,5,'Customer ID:',0,0);
$pdf->Cell(34 ,5,'0012',0,1);/*end of line*/
$pdf->Cell(130 ,5,'Delhi, 751001',0,0);
$pdf->Cell(25 ,5,'Invoice Date:',0,0);
$pdf->Cell(34 ,5,'12th Jan 2019',0,1);
$pdf->Cell(130 ,5,'',0,0);
$pdf->Cell(25 ,5,'Invoice No:',0,0);
$pdf->Cell(34 ,5,'ORD001',0,1);
$pdf->SetFont('Arial','B',15);
$pdf->Cell(130 ,5,'Bill To',0,0);
$pdf->Cell(59 ,5,'',0,0);
$pdf->SetFont('Arial','B',10);
/*make a dummy empty cell as a vertical spacer*/
$pdf->Cell(189 ,10,'',0,1);
/*make a dummy empty cell as a vertical spacer*/
$pdf->Cell(50 ,10,'',0,1);

$pdf->SetFont('Arial','B',10);

$pdf->Cell(10 ,6,'Sl',1,0,'C');
$pdf->Cell(80 ,6,'Description',1,0,'C');
$pdf->Cell(23 ,6,'Qty',1,0,'C');
$pdf->Cell(30 ,6,'Unit Price',1,0,'C');
$pdf->Cell(20 ,6,'Sales Tax',1,0,'C');
$pdf->Cell(25 ,6,'Total',1,1,'C');
/*Heading Of the table end*/
$pdf->SetFont('Arial','',10);
    for ($i = 0; $i <= 10; $i++) {
		$pdf->Cell(10 ,6,$i,1,0);
		$pdf->Cell(80 ,6,'HP Laptop',1,0);
		$pdf->Cell(23 ,6,'1',1,0,'R');
		$pdf->Cell(30 ,6,'15000.00',1,0,'R');
		$pdf->Cell(20 ,6,'100.00',1,0,'R');
		$pdf->Cell(25 ,6,'15100.00',1,1,'R');
	}
		

$pdf->Cell(118 ,6,'',0,0);
$pdf->Cell(25 ,6,'Subtotal',0,0);
$pdf->Cell(45 ,6,'151000.00',1,1,'R');


$pdf->Output();

?>
        

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

class PDF_Rotate extends FPDF
{
var $angle=0;

function Rotate($angle,$x=-1,$y=-1)
{
    if($x==-1)
        $x=$this->x;
    if($y==-1)
        $y=$this->y;
    if($this->angle!=0)
        $this->_out('Q');
    $this->angle=$angle;
    if($angle!=0)
    {
        $angle*=M_PI/180;
        $c=cos($angle);
        $s=sin($angle);
        $cx=$x*$this->k;
        $cy=($this->h-$y)*$this->k;
        $this->_out(sprintf('q %.5F %.5F %.5F %.5F %.2F %.2F cm 1 0 0 1 %.2F %.2F cm',$c,$s,-$s,$c,$cx,$cy,-$cx,-$cy));
    }
}

function _endpage()
{
    if($this->angle!=0)
    {
        $this->angle=0;
        $this->_out('Q');
    }
    parent::_endpage();
}
}
?>