You can just execute the page like any other by looking into fsockopen or depending on PHP configuration could use either fopen, file etc, but basically you will need to load the page as if you executed it in the browser
example
//fopen example
$fp = @fopen("http://mydomain.com/php.php","r");
if (!$fp)
die("Couldnt get a connection to file");
else
{
//read the file by using fread, fgets etc
}