I don't actually have a problem, but i'm not sure why not?
I used php includes to add a footer and top menu on all my pages, so that I can change them easily. I was expecting that i would then have to change all the .html files to .php, but i didnt. It works fine and its very handy to still be able to check new content locally on the html file before uploading(although without the includes).
Did i just get lucky or does this always work like that?