No, Windows and Ubuntu are completely separate things, whether you install it or run a live session. You can also install Ubuntu without removing Windows, and in that case, you'll just choose between Windows and Ubuntu at startup. When you run Ubuntu, it will be as if you don't have Windows installed and when you run Windows, it will be as if you don't have Ubuntu installed. Actually, Windows isn't even capable of knowing that you have installed Ubuntu at all. It will look to Windows as if the harddisk har shrunk in size. Ubuntu is able to read Windows' filesystems, though, so you can access Windows-files in Ubuntu, but not Ubuntu-files in Windows. One benefit of that, is that even if something happens to your Windows-install that makes it unusable, because of malware, or something like that, Ubuntu will still work as good as ever. That malware would also not be able to "infect" Ubuntu in any way.
You should also note that there is nothing in Ubuntu that requires permission, registration or anything like that -- including the installed office application; LibreOffice. It is also very compatible with MS Office. If you install Ubuntu, it will run much faster than the live session.