My need is that I upload two image files and that should be added to an existing PDF file. I have read about FPDF, basing on that I have followed this post link. In case if somebody can post a simple working example/link it would be helpful for searchers like me and some more people who would also take the same route to find some helpful answers.
It seems there is an extension called FPDI for FPDF. Here is a blog post about how to modify an existing pdf: http://pranavom.wordpress.com/2011/03/15/modify-pdf-using-fpdffpdi-library/
You can place an image using FPDI like so:
$pdf = new FPDI();
$pdf->AddPage();
$pdf->setSourceFile("MySource");
$template = $pdf->importPage(1);
$pdf->useTemplate($template);
$pdf->Image('MyImage.jpg', $x, $y, $width, $height);
$pdf->Output($outputPath, "F");