Pages module

 * Provide Slug managed urls ( Semantic URLs / user-friendly / seo-friendly / RESTful-urls )
 * Slug is part of URL which identifies a page using human-readable keywords.
 * It is usually the end part of the URL.
 * .. short name given to an article ..

- frontend - show content by slug urls
- backend - CRUD / list / create+edit forms
(migration, templates, routes )

используй:
return throw new \Symfony\Component\HttpKernel\Exception\NotFoundHttpException('Not Found 404');