PHP: Include file
The include function is useful for streamlining code across your site. Rather than the full code of you header section, for example, you can replace it the one line of code required for the include function. This is also advantageous for future modifications. This does not affect SEO (Search Engine Optimization) since search engines only detect the parsed code (output i.e. what you see in the source code).
<?php include(“somefolder/somedocument.html”); ?>