Use the #include directive to include files in your current html documents. The "file=" or "virtual=" elements can both be used.
For example, let's say you were trying to include doc1.html in doc2.html. Both documents exist in a directory called "docdir". Below is the code that you would insert in doc2.html.
File Include Method:
<!--#include file="doc1.html"-->
Virtual Include Method:
<!--#include virtual="/docdir/doc1.html"-->
