Help with theme and pages

I’m trying to figure out how to wrap my WordPress theme around an existing page that is not in WordPress. The existing page is on an outside webpage that I have the link to (I’m licensed for the content) and I want it to appear to be part of my WordPress theme and site. I’ve used iframes in the past to do this before switching to WordPress but realize that is not a good solution. If anyone can point me to the documentation for doing this or give me the rundown on how to do this I would greatly appreciate it as I’m on a deadline!

Thanks!!