I use several php files but to keep everything in good format for SEO(search engine optimization) I am using this in my htaccess.
AddType application/x-httpd-php .html
This allows normal html pages run as a php page. And this is to include an outside php file.
<?php $ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "YOUR-LINK");
curl_setopt($ch, CURLOPT_HEADER, 0);