“wpcfe_bulk_assign_form_content” hook is used to add custom styles to print PDF Template

function custom_assign_client_callback( $shipment_id ){
    $wpcargo_client 	= wpcfe_get_users('wpcargo_client');
    if( can_wpcfe_assign_client() ): ?>
        <div class="form-group">
            <div class="select-no-margin">
                <label><?php esc_html_e('Client','wpcargo-frontend-manager'); ?></label>
                <select name="registered_shipper" class="wpcfe-select mdb-select mt-0 form-control browser-default" id="registered_client" >
                    <option value=""><?php esc_html_e('-- Select Client --','wpcargo-frontend-manager'); ?></option>
                    <?php if( !empty( $wpcargo_client ) ): ?>
                        <?php foreach( $wpcargo_client as $key => $value ): ?>
                            <option value="<?php echo $key; ?>" <?php selected( get_post_meta( $shipment_id, 'registered_shipper', TRUE ), $key ); ?>><?php echo $value; ?></option>
                        <?php endforeach; ?>	
                    <?php  endif; ?>	                
                </select>
            </div>
        </div>
    <?php endif;
} 

add_action( 'wpcfe_bulk_assign_form_content', 'custom_assign_client_callback', 10, 1 );