Running Windows 10 from bootable DVD without installing on hard disk? I am trying to boot from a Windows 10 DVD, but it says something about installing it.

I don't want to replace my existing OS with Windows 10. I just want to use some software with it. How do I do that?
In order to use Windows you must first install it, you can't just boot from a CD and expect it to work. While that may be possible with some varieties of Linux, it is not with Windows (or macOS).

In order for us to help you you absolutely must provide the model of Mac you have and what version of macOS is installed on it. Edit your question and put that info there.