mergeDocuments example

$files = [];
        $models = $this->getOrderDocumentsQuery($data->orders, $data->docType)->getResult();
        foreach ($models as $model) {
            foreach ($model->getDocuments() as $document) {
                $file = $this->downloadFileFromFilesystem(sprintf('documents/%s.pdf', $document->getHash()));
                if ($file !== null) {
                    $files[] = $file;
                }
            }
        }

        $this->mergeDocuments($files);

        // Remove temporary files         foreach ($files as $file) {
            unlink($file);
        }
    }

    /** * The sendMailAction fired from the batch window in the order backend module when the user want to send the order * status mail manually. * * @return void */