Actually, php is able to be parsed in many files such as .html .htm .css .js .shtml and many more, however it depends on your web server settings. A lot of hosts dont parse php unless its in a .php file.
If your not sure if you have php running on your hosting, make a file called "test.php" and enter the following:
Code:
<?php
phpinfo();
?>
Upload it and view it in IE, if php is installed you will see a page with all the php settings and version info, if not, you dont have it installed.