[PHP] invoking the PHP engine on a single .html file

[Krzysztof Wozniak]

Is there any possibility to invoke the PHP engine on a single, specific
file? I mean, I know I can ask PHP politely to treat every .html file as
a PHP file, but it will slow down the whole server. Can the PHP engine
be invoked locally (by folder) or preferably on a single file? 
 
Thanks,
 
Krzysztof