TL;DR version: here’s how to parse HTML files with PHP hypertext preprocessor on apache 2.4x webserver, and PHP7 on linux
In PHP 7, the newest and ever more popular version of the PHP scripting language, the only files that are parsed by default are the ones that have .php, .phtml, or .php3/php4/php5 extensions. I don’t know who might still be using .php3, .php4 (never seen anyone use this one), or .php5 file extensions, but I’m sure many of you still usually use HTML files, and want to insert some PHP code into it.
Obviously, even though a lot of discussion is against the practice of parsing HTML files with PHP, you might still need this option. Regardless of whether you are a beginner or a pro in the art of website creation, scripting, web programming and alike, you still need to be able to parse files with the HTML or HTM extension, as PHP files, because integrating some PHP code into HTML and viceversa, it’s the easieast way to quickly test out something in a browser. So set aside the “best practices” pride for now, and just accept it as a fact that a lot of people still need this option 🙂