Include It is a little old, consider to use
Include Me instead: it has the same features
but it uses the WordPress short code standards. You can read more on the
Incude Me official page.
Include It is a plugin that permits the inclusion, in a post or in a page, of any type of file (even a php script that will be executed).
I use it to write some functionalities needed in some pages, without creating special template pages (that are theme dependant)
and without using a "php code executor".
The inclusion can be forced to be within an IFRAME html tag.
See the options page of the plugin for a deeper explanation and how to use it and the
plugin official page.
Upload the plugin folder into your "wp-content/plugins".
Log in to Wordpress Administration area, choose "Plugins" from the main menu, find "Include",
and click the "Activate" button.
Go to the options page and read the usage explanations.