Assuming you are using asp.net
(depending on the complexity of scripts on the source page, as code behind) but if you are simply trying just to display info this might work.
Create a blank new asp.net page
in the code behind use
WebClient webClient = new WebClient();
string htmlString = w.DownloadString("https://www.thatpage.com");
Then use the asp.net response.write command to write the entire string into the page then you can now iframe reference the asp.net page you just created and it should display fine.