You can use following code in .htaccess file to parse php pages in html pages

RemoveHandler .html .htm
AddType application/x-httpd-php .php .htm .html

To can check above code is working ir not? by creating one test page with following code

root@gunjan[~]#pico test.html

< html>
< head>
< body>
< h1>
< ?php echo “WORKING FINE!”; ?>
< /h1>
< /body>
< /html>