PHP - How to use mPDF to merge PDFs

Question

I will start out by saying that I can generate PDFs just fine with mPDF, but for the life of me, I can\'t get it to merge an existing PDF with the PDF it just generated.

Answer 1

function mergePDFFiles(Array $filenames, $outFile) {
    $mpdf = new mPDF();
    if ($filenames) {
        //  print_r($filenames); die;
        $filesTotal = sizeof($filenames);
        $fileNumber = 1;
        $mpdf->SetImportUse();
        if (!file_exists($outFile)) {
            $handle = fopen($outFile, 'w');
            fclose($handle);
        }
        foreach ($filenames as $fileName) {
            if (file_exists($fileName)) {
                $pagesInFile = $mpdf->SetSourceFile($fileName);
                //print_r($fileName); die;
                for ($i = 1; $i <= $pagesInFile; $i++) {
                    $tplId = $mpdf->ImportPage($i);
                    $mpdf->UseTemplate($tplId);
                    if (($fileNumber < $filesTotal) || ($i != $pagesInFile)) {
                        $mpdf->WriteHTML('');
                    }
                }
            }
            $fileNumber++;
        }
        $mpdf->Output($outFile, 'D');
    }
}