Applying watermarks on pdf files when users try to download the files

Question

Hey guys, the solutions for my schools' assignments all have waterstamps on the pdfs with our username on it. I was wondering if you guys know how to do something like that using php? Do they run a script prior to the download process?

Thanks

Answer 1

There is an excellent opensource php library http://www.tcpdf.org/ , I use it for all pdf generating tasks.

Answer 2

Although there are several very good PDF libs for PHP, if I were writing such a program I'd just shell out to run pdftk but you' still need to generate your watermark.

$tempfile=tempnam();
system("pdftk input_file.pdf background watermark.pdf output $tempfile dont_ask", $errcode);
if (!$errcode && $ih=fopen($tempfile, 'r')) {
    header('Content-Type: application/pdf');
    fpassthru($ih);
    fclose($ih);
} else {
    print "Whoops";
}
unlink($tempfile);