Message: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\CodeIgniter\system\application\models\your_model.php:23)
Filename: tcpdf/tcpdf.php
Line Number: 7996
TCPDF ERROR: Some data has already been output to browser, can’t send PDF file
Well, error means that somewhere - before the line:
$this->pdf->Cell(0, 12, $pdf_data, 1, 1, 'C');
you are already sending data to the screen. Also, it still says that you are sending output in your_model.php on line 23... So error is somewhere in your model
Try to add this to your model (and see if you get results):
instead of return $result;
do:
print_r($result); exit;