HOW TO RUN PHP IN HTML FILE

1. Determine which php version running on your server

#php -v

2. Determine configuration of Apache PHP Handler, is it dso or cgi or SuPHP

#/usr/local/cpanel/bin/rebuild_phpconf --current

dso - mean that php run as Apache module

cgi or SuPHP - php run as a CGI module

Then we can add the following  to .htaccess according to this,

For dso(php as Apache module) 

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

For SuPHP, if your server run php4

AddType application/x-httpd-php4 .htm .html

or

AddType application/x-httpd-php5 .htm .html

If your server run php5

For CGI , add to .htaccess line 

AddHandler application/x-httpd-php4 .html .htm

or

AddHandler application/x-httpd-php5 .html .htm

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AddType application/x-httpd-php(x) - for php as Apache module, Dso. x - php version 

AddHandler application/x-httpd-php(x) - for php as CGI. x - php version