not work in "send-pdf-for-contact-form-7 plugin"

I want to add a unique number in contact-form-7, user will receive a notification email and pdf file attachments after submited the form.

I use the “send-pdf-for-contact-form-7 plugin” to create pdf files.
I tried using a simple php function to generate a unique number.

/* Generate Quote Ticket */
function genTicketString() {
    $length = 8;
    $characters = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    for ($p = 0; $p < $length; $p++) {
        $string .= $characters[mt_rand(0, strlen($characters)-1)];
    }
    return $string;
}
add_shortcode('quoteticket', 'genTicketString');

I got code from This link

[dynamictext ticket “quoteticket”] The shortcode works well on the form but doesn’t work on pdf file using “send-pdf-for-contact-form-7 plugin”

please help .

https://www.ads-software.com/plugins/contact-form-7-dynamic-text-extension/