If it’s ordinary HTML page, you can include via an <iframe>
–ugly, clunky, and not necessarily good for performance, but it should work.
It it’s built in PHP, you can use an include
statement in a PHP widget, depending on how your server is configured.
Of course, a lot depends on the software that page is using. If it’s just javascript you could drop that directly into a text widget.
It’s difficult to be more precise without:
* A link to the page in question
* Knowing what software you are talking about
* Seeing what that software is outputting.
Moved to Support.