PHPExcel create pdf from a template - codeigniter

Question

I would like to generate a pdf file using php excel from a template using the following code :
//load our new PHPExcel library
$this->load->library('excel');
echo 'Library load succesfull';
//name the worksheet
$objPHPexcel = PHPExcel_IOFactory::load('/Applications/MAMP/htdocs/timesheet/files/Timesheet_template.xlsx');
echo 'Loading template successfull...';
$objWorksheet = $objPHPexcel->getActiveSheet();
$objWorksheet->getCell('C17')->setValue($td_3);
$objWorksheet->getCell('D17')->setValue($td_4);
$objWorksheet->getCell('E17')->setValue($td_5);
$objWorksheet->getCell('F17')->setValue($td_6);
$month = date('F');
$year = date('Y');
$data['user_data'] = $this->session->userdata('user');
$user_id = $data['user_data']["employee_id"];
$f_name = $data['user_data']["f_name"];
$s_name = $data['user_data']["s_name"];
$username = $data['user_data']["user_name"];
$title = $data['user_data']["title"];
$is_active = $data['user_data']["is_active"];
$employee_type = $data['user_data']["employee_type"];
// $filename = 'just_some_random_name.xlsx'; //save our workbook as this file name
//save it to Excel5 format (excel 2003 .XLS file), change this to 'Excel2007' (and adjust the filename extension, also the header mime type)
//if you want to save it as .XLSX Excel 2007 format
echo 'ALMOST CREATING THE PDF FILE';
$objWriter = PHPExcel_Settings::PDF_RENDERER_DOMPDF;
$rendererLibrary = 'domPDF0.6.0beta3';
$rendererLibraryPath = '/Applications/MAMP/htdocs/timesheet/system/helpers/dompdf';
$objWriter = PHPExcel_Settings::PDF_RENDERER_DOMPDF;
$rendererLibrary = 'domPDF0.6.0beta3';
$rendererLibraryPath = '/Applications/MAMP/htdocs/timesheet/system/helpers/dompdf';
if (!PHPExcel_Settings::setPdfRenderer(
$objWriter, $rendererLibraryPath
)) {
die(
'Please set the $rendererName and $rendererLibraryPath values' .
PHP_EOL .
' as appropriate for your directory structure'
);
}
echo 'pdf creation almost starting';
// $objWriter = PHPExcel_IOFactory::createWriter($objPHPexcel,'pdf');
$objWriter = new PHPExcel_Writer_PDF($objPHPexcel);
echo 'SUCCESS FULLY CREATED THE PDF FILE...';
$under_score = "_";
$year = preg_replace('/\s+/', '', $year);
$inputFileType = $username . $under_score . $month . $under_score . $year . ".pdf";
$objWriter->save("files/un_approved/" . $username . $under_score . $month . $under_score . $year . ".pdf");
I am using dompdf library to convert the final template to pdf but the file that's generated comes as corrupted and cannot be opened by Adobe Reder. Please advise what is the best way I should approach it?