in other words, how can I copy paste a full page from a html site to wordpress and retain the html format and look so to a casual visitor it looks a html page? Is It possible?
You can try to customize the page to look like a normal website by using themes and removing the sidebar etc yes you can copy paste html in to WP posts and pages to look exactly like the source.
Well... you can copy html, that is true, but if you copy an existing HTML-page, verbatim, it will contain a lot of code that you do NOT want to double-post on your page. You'll end up with double up with doctype, html, head, body and so forth. Not recommended. If you want to copy a page, why not just store it as an .html-file and link to it from somewhere in your WP-install? I don't really see the point of doing anything like this (not anything legal, at least), so it would probably help if you tell us WHY you want to do this. I'm guessing you're either trying to do something less than legal, or you're trying to do something the wrong way.
I had a client a few years ago who was selling blogs to people who had their own websites. My job was to make the blog look like their existing site. Some of them I wouldn't even show you (if they still existed) because the original site was so appalling. However unless you viewed the source really, really closely you'd never have guessed the site was a blog or wordpress. check this one out It's from the same era. Static home page, almost every page is a page and not a post. Custom plugins. IMO it doesn't look like WP.
You can basically make Wordpress look like whatever you want. I seem to remember there being a plugin / cache-builder that allowed you to create static .html-files for every post/page too, to completely throw off anyone looking for .php in the filenames - for no good reason at all, of course, but hey.
Couldn't you just iframe the page? I use a commercial plugin that iframes another Wordpress blog, but if it was HTML no one would know the difference. You don't need a plugin, just create a post or page and in the "Text" screen add the iframe code if your template has a blank template.