Can't find httpd.conf

buntu doesn't use httpd.conf as standard, instead global configuration stuff for apache is found in /etc/apache2/apache2.conf. You can create a httpd.conf in the apache2 directory, and load any further configuration from it by including the following line in /etc/apache2/apache2.conf.

Include /etc/apache2/httpd.conf

You don't need that file to configure apache, but you can create it if other software relies on it being there.