Apache setup for not found page

How to make this?:

http://www.example.com/abcd/some.html

document root is:

/web/example/html/

if the file /abcd/some.html does not exists, take it from:

/main/pages/html/abcd/some.html

how to make this?

 

Edit httpd.conf and edit <virtual host> of the user to use /main/pages/html/ instead of /web/example/html/

then service httpd restart

 

Or simply add this to your .htaccess

ErrorDocument 404 /404page.html

Code (markup):

And customize your 404page.html in a way you like.