Using .htaccess to redirect user to 404 page when ever an invalid url is enter.

To do this is very simple Follow the steps below.

ErrorDocument 404 /404.php

The code should look like this

# HTID:15003771: DO NOT REMOVE OR MODIFY THIS LINE AND THE LINES BELOW
php_value display_errors 1
# DO NOT REMOVE OR MODIFY THIS LINE AND THE LINES ABOVE HTID:15003771:
ErrorDocument 404 /404.php

Note: to add redirect to 404 page on each folder, you have to add .htaccess to each folder.