Possible to Insert One HTML Doc Into Another?

[Bongolation]

Is it possible to load an HTML document into the main HTML document, much like inserting a graphic?

Could one have, say, a "header.htm" file that could be coded into any page on my site?

If this is a dumb question, sorry, but it's the only work-around I can think of for a problem I'm trying to figure out.

 

[Bongolation]

Never mind.

I figured out how to do it with SSI or PHP.