README

You have to name your config file:
    /var/wwww/vhosts/example.com/conf/vhost.conf

After doing so, you need to regenerate the apache config file from plesk:
    /usr/local/psa/admin/sbin/websrvmng -u --vhost-name=example.com

And afterwards reload apache configuration:
    /etc/init.d/httpd reload