Dynamically send pdf attached to post with contact form 7 [2]

I'm come from this post : contact form 7

So i do the same exact code :

    add_action('wpcf7_before_send_mail', 'my_dynamic_attachments');

function my_dynamic_attachments($cf7) {
    $id = $cf7->id();
    $upload_dir = wp_upload_dir('2015/03');
    if ($id==1326){
        $submission = WPCF7_Submission::get_instance();
        $data = $submission->get_posted_data();
        $pdf = $data['brochures'][0];
        //echo $pdf;
        $submission->add_uploaded_file('pdf', $upload_dir['path'].'/'.$pdf);
    }
}

The problem is if file is sent only i uncomment the "echo". Since he was comment, file not be sent and i don't understand why ...

Have an idea ?

Thanks