fluentform-email-attachment.php

<?php
/*
* Add Attachment to the email notification dynamically.
* @param $attachments array - Array of the attachments.
* @param $notification array - Email Notification array
* @param $form object - The Form Object
* @param $data array - The input submission data
* @return array 
*/

add_filter('fluentform_filter_email_attachments', function ($attachments, $notification, $form, $data) {
    if ($form->id != 91) {  // Add your form id here
        return $attachments;
    }
    /*
    * You can check if $form or $notification and based on that push your file.
    */
  
    $pathToYourFile = WP_CONTENT_DIR.'YOURFILE_PATH/file.pdf'; // Add path to your file
    $attachments[] = $pathToYourFile; //
    return $attachments;
}, 10, 4);