public function importPages(string $filePath): PdfInterface
    {
        if (!is_file($filePath)) {
            throw new \InvalidArgumentException(sprintf('The file "%s" does not exist.', $filePath));
        }
        $numberPagesCurrentFile = count($this->mpdf->pages);
        $numberPagesExternalFile = $this->mpdf->setSourceFile($filePath);
        $numberTotalPages = $numberPagesCurrentFile + $numberPagesExternalFile;
        $this->mpdf->setImportUse();

        for ($i = 1; $i <= $numberPagesExternalFile; $i++) {
            if ($i < $numberTotalPages) {
                $this->mpdf->addPage();
            }
            $this->mpdf->useTemplate($this->mpdf->importPage($i));
        }

        return $this;
    }