How to navigate to a new page and download a yii2 file at the same time?

Question

Yii

My code snippet, but if the first if is not executed, the transition to the desired page does not occur, but only the file is downloaded. How to get around this?

if($this->flag == 1){               
                Yii::$app->mailer->compose()
                    ->setTo($this->email)
                    ->setFrom(['@gmail.com' => Yii::$app->params['senderName']])
                    ->setReplyTo([$this->email => $this->fromPerson])
                    ->setSubject("Ваш конверт")                                  
                    ->attachContent($pdf->Output('', 'S'), ['fileName' => 'pdfName.pdf',   'contentType' => 'application/pdf'])
                    ->send();                                
            }            
            header('Content-Type: application/octet-stream');
            header('Content-Disposition: attachment; filename=' . 'enelope.pdf');
            exit($pdf->Output('', 'S'));  // работает не коорректно, не переводит на нужную страницу