You need to set the php parser to be able to parse .html extensions. You do this by setting an Apache (or other server) handler to parse .html extensions with x-httpd-php
For CPanelX:
In the main admin area, go to “Apache Handlers”. Then to add it, under “Extensions” type:
.html
…then under “Handler” type:
x-httpd-php
…then click Add of course and viola. All your html extension files will now be parsed by the php processor if there’s any php code in them. I’m pretty sure this is what you’re looking for. Hope it helps.