You can find full step by step implementaion on http://phpclicks.com/mpdf-library-using-codeigniter/
Place the mpdf library in thirdparty directory and Create the mpdf.php file to create a wrapper class for codeigniter by placing following code and put that file into Codeigniter application/library directory.
if (!defined('BASEPATH')) exit('No direct script access allowed');
include_once APPPATH.'/third_party/mpdf/mpdf.php';
class M_pdf {
public $param;
public $pdf;
public function __construct($param = "'c', 'A4-L'")
{
$this->param =$param;
$this->pdf = new mPDF($this->param);
}
}
In your controller you can use below code by placing your own pdf data.Uploads directoy is your root directory you can update your own path.
$filename = time()."_order.pdf";
$html = $this->load->view('unpaid_voucher',$data,true);
// unpaid_voucher is unpaid_voucher.php file in view directory and $data variable has infor mation that you want to render on view.
$this->load->library('M_pdf');
$this->m_pdf->pdf->WriteHTML($html);
//download it D save F.
$this->m_pdf->pdf->Output("./uploads/".$filename, "F");