Send mpdf output as attachment email file with PHPMailer in Codeigniter - codeigniter

Question

I have pdf file created with mpdf library and I want to send the output file as attachment in email with PHPMailer. I have tried this code but still not working. The attachment is missing but the email is successfully sent.
This is my code in controller :
public function pdf_file()
{
$this->load->library('m_pdf');
$this->data['title']="MY PDF TITLE 1.";
$this->data['description']="Test PDF File";
$html=$this->load->view('frontend/pdf_output',$this->data, true);
$pdfFilePath = "the_pdf_output.pdf";
$pdf = $this->m_pdf->load();
$pdf->SetProtection(array('copy'), '123456', '123456', 128);
$pdf->SetVisibility('screenonly');
$pdf->WriteHTML($html,2);
//$pdf->Output($pdfFilePath, "D");
$content = $pdf->Output('', 'S');
$content = chunk_split(base64_encode($content));
$subject = "PDF File";
$message = $this->load->view('frontend/pdf_output',$this->data,TRUE);
$from = "aaa#yahoo.com";
$to = 'xxx#gmail.com';
$cc = null;
$attachment = $content;
$sender = "Administrator";
$site_url = site_url();
if ($site_url == 'http://localhost/mysite/')
{
$this->load->view('frontend/email',$data);
}
else
{
$this->booking_model->send_email($subject,$message,$from,$to,$cc,$attachment,$sender);
}
}
This is my PHPMailer configuration :
function send_email($subject,$message,$from,$to,$cc,$attachment,$sender)
{
$this->load->library('PHPMailerAutoload');
$mail = new PHPMailer;
$mail->isSMTP();
$mail->SMTPDebug = 0;
$mail->Debugoutput = 'html';
$mail->SMTPOptions = array(
'ssl' => array(
'verify_peer' => false,
'verify_peer_name' => false,
'allow_self_signed' => true
)
);
$mail->Host = "mail.host.com";
$mail->IsHTML(true);
$mail->Port = 26;
$mail->SMTPAuth = true;
//$mail->SMTPSecure = 'ssl';
$mail->Username = "aaa#domain.com";
$mail->Password = "123456";
$mail->setFrom($from, $sender);
if (count($cc) > 1)
{
for ($i=1; $i <= count($cc); $i++)
{
$mail->addCC($cc[$i], $sender);
}
}
if (!empty($attachment))
{
$mail->addAttachment($attachment);
}
$mail->addAddress($to);
$mail->Subject = $subject;
$mail->msgHTML($message);
//send the message, check for errors
if (!$mail->send()) {
// failed
} else {
// success
}
}
Anyone know to send the pdf attachment on email ? Please help.