Simple class that extends FPDI/FPDF to build PDF files using a file-based buffer instead of the default the in-memory buffer.

Allows much much larger PDF documents to be built.

Adapted from http://www.fpdf.org/en/script/script76.php to extend FPDI.

I have used this class to produce a 10k page PDF document with custom page numbering using less than 256MB of php memory.

Requires setasign/fpdi-fpdf:

composer require setasign/fpdi-fpdf

My example usage scenario:

Need to merge 1000 individual pdfs into a single large pdf and number each page

$mergeFile = '/tmp/merged.pdf';
$totalPages = 0;
$pageNum = 0;

// Count the total number of pages across all PDFs being merged
foreach ($this->pdfs as $pdf) {
    $totalPages += (new Fpdi())->setSourceFile($pdf);
}

$fpdi = new FPDI2File();
$fpdi->Open($mergeFile);
foreach ($this->pdfs as $pdf) {
    $pageCount = $fpdi->setSourceFile($pdf);
    for ($i = 1; $i <= $pageCount; $i++) {
        $pageNum++;

        $template = $fpdi->importPage($i);
        $size = $fpdi->getTemplateSize($template);
        $fpdi->AddPage(
            $size['width'] > $size['height'] ? 'L' : 'P',
            [$size['width'], $size['height']]
        );
        $fpdi->useTemplate($template);

        // Disable page breaking so we can set numbers at the bottom of the page.
        $fpdi->setAutoPageBreak(false);

        // Add the page numbering.
        $paging = "Page $pageNum of $totalPages";
        $fpdi->SetXY($size['width'] - ceil(strlen($paging) * 2.7), $size['height'] - 10);
        $fpdi->SetFont('Arial', '', 7);
        $fpdi->Write(0, $paging);

        // Add document number
        $fpdi->SetXY(15, $size['height'] - 10);
        $fpdi->SetFont('Arial', '', 7);
        $fpdi->Write(0, 'XXX_YYY');
    }
}

$fpdi->Output();