using ob_get_content(9 for TCPDF

Hi
I have used ob_start() in CFv5 without problems to avoid issues with php code in TCPDF module,
but in CFv6 i have not succeed changing $form->data['file_pdf'] by $this->data['file_pdf']
although when I define something like $this->data['date']=date('Y-m-d'); get registered as var without issues
I apreciate if someone can help me
​
ob_start();
<?php
..............my code
?>
$form->data['file_pdf'] = ob_get_contents();
ob_end_clean();