Not using iframes puts you in a world of handling #document security issues with cross domain and links firing unexpected ways that was not intended for originally, do you really need bad Advertisements?
You can use jquery .load function to send the page to whatever html element you want to target, assuming your not getting this from another domain.
You can use javascript .innerHTML value to set and to rewrite the element with whatever you want, but if you add another file you might be writing against 2 documents in 1... like a in another
iframes are old, another way we can add "src" into the html alone without any use for javascript. But it's old, prehistoric, and just plain OLD! Frameset makes it worse because I can put #document in those to handle multiple html files. An Old way people created navigation menu's Long and before people had FLIP phones.
1.) Yes you will have to work in Javascript if you do NOT want to use an Iframe.
2.) There is a good hack in which you can set the domain to equal each other without having to set server stuff around. Means you will have to have edit capabilities of the documents.
3.) javascript window.document is limited to the iframe itself and can NOT go above the iframe if you want to grab something through the DOM itself. Because it treats it like a separate tab, it also defines it in another document object model.