[php] Merge PDF files with PHP

I've had similar problem in my software. We've wanted to merge several PDF files into one PDF file and submit it to an outer service. We've been using the FPDI solution as shown in Christa's solution.

However, the input PDF's we've been using could be in version higher than 1.7. We've decided to evaluate the FPDI commercial add-on. However, it turned out that some of the documents scanned by our office copier were having malformed indexes, which crashed the commercial FPDI add-on. So we've decided to use Ghostscript solution as in Chauhan's answer.

But then we got some strange metadata in the output PDF properties.

Finally we've decided to join two solutions to get PDF's merged and downgraded by Ghostscript, but the metadata is set by FPDI. We don't know yet how it would work with some advanced formatted pdfs, but for scans we use it works just fine. Here's our class excerpt:

class MergedPDF extends \FPDI
{
    private $documentsPaths = array();

    public function Render()
    {
        $outputFileName = tempnam(sys_get_temp_dir(), 'merged');

        // merge files and save resulting file as PDF version 1.4 for FPDI compatibility
        $cmd = "/usr/bin/gs -q -dNOPAUSE -dBATCH -dCompatibilityLevel=1.4 -sDEVICE=pdfwrite -sOutputFile=$outputFileName";
        foreach ($this->getDocumentsPaths() as $pdfpath) {
            $cmd .= " $pdfpath ";
        }
        $result = shell_exec($cmd);
        $this->SetCreator('Your Software Name');
        $this->setPrintHeader(false);
        $numPages = $this->setSourceFile($outputFileName);
        for ($i = 1; $i <= $numPages; $i++) {
            $tplIdx = $this->importPage($i);
            $this->AddPage();
            $this->useTemplate($tplIdx);
        }

        unlink($outputFileName);

        $content = $this->Output(null, 'S');

        return $content;
    }

    public function getDocumentsPaths()
    {
        return $this->documentsPaths;
    }

    public function setDocumentsPaths($documentsPaths)
    {
        $this->documentsPaths = $documentsPaths;
    }

    public function addDocumentPath($documentPath)
    {
        $this->documentsPaths[] = $documentPath;
    }
}

The usage of this class is as follows:

$pdf = new MergedPDF();
$pdf->setTitle($pdfTitle);
$pdf->addDocumentPath($absolutePath1);
$pdf->addDocumentPath($absolutePath2);
$pdf->addDocumentPath($absolutePath3);
$tempFileName = tempnam(sys_get_temp_dir(), 'merged');
$content = $pdf->Render();
file_put_contents($tempFileName, $content);