Source code for https://victorfont.com/formidable-pro-rename-upload-file/

rename_image.php

<?php

add_filter('sanitize_file_name', 'rename_image', 10, 2);
function rename_image($filename, $filename_raw) {
	if ($_POST['form_id'] == '6') {
		$firstname = $_POST['item_meta'][83] . '-';
		$lastname = $_POST['item_meta'][84] . '-';
		$category = $_POST['item_meta'][88] . '-';
		$imagename = $_POST['item_meta'][85] . '-';
		$assigned = $_POST['item_meta'][86] . '-';
		$print = $_POST['item_meta'][87];
		$info = pathinfo($filename);
		$ext = empty($info['extension']) ? '' : '.' . $info['extension'];
		$new = $firstname . $lastname . $category . $imagename . $assigned . $print . $ext;
		if( $new != $filename_raw ) {
			$new = sanitize_file_name( $new );
		}
		return $new;
	} else { 
		return $filename;
	}
}