standard 404 html response

I have created a web server. There are certain pages that I would like to return the standard 404 error to the user (even though the pages exist in my browser). I have seen many articles on how to make custom 404 error pages, but I specifically want to return the standard error page (on certain pages that do indeed exist), like when someone is browsing the internet and types an internet address that doesn't exist. thanks in advance.