File Extension PHP4 File Format PHP 4 file PHP4 stands for PHP 4 file. This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question Add downloadable, member-protected files on website How can I add an IF statement to a .php file MYSQL/PHP based CMS (Mambo,Joomla) on the 400.