PHPExcel和Mpdf不生成文件

Question

我使用PHPExcel生成模板，然后我希望使用Mpdf将其转换为PDF文件。我使用PHPExcel 1.7.8和Mpdf 6.0

但问题在于

1. 未生成PDF文件
2. 浏览器想要显示生成的文件。

我的代码

    $rendererName = PHPExcel_Settings::PDF_RENDERER_MPDF;
    $rendererLibrary = 'mpdf';
    $rendererLibraryPath = APPPATH.'plugins/' .
    $rendererLibrary;
    if (!PHPExcel_Settings::setPdfRenderer(
                 $rendererName,
                 $rendererLibraryPath
           )) {
           die(
                 'Please set the $rendererName and $rendererLibraryPath values' .
                 PHP_EOL .
                 ' as appropriate for your directory structure'
    ); }

    $filename = "DWG Register.pdf"; //save workbook to a file name

    header('Content-Type: application/pdf'); //mime type
    header('Content-Disposition: attachement;filename="'.$filename.'"'); //tell browser what's the file name
    header('Cache-Control: max-age=0'); //no cache

    $objWriter = PHPExcel_IOFactory::createWriter($this->excel, 'PDF');          
    $objWriter->setSheetIndex(0);
    $objWriter->save('php://output');
    exit;