You can install Windows 10 on a Chromebook but you'll require another system for preparation.
Anyway, why would you want to install Windows on a Chromebook? They're designed to use ChromeOS, it comes with the package for it to be a secure environment. ChromeOS has less attack vectors than Windows, OS X and traditional Linux because it provides less usability and features which are enabled/supported, it's also a custom Linux (all Google's OS's are, including Android).
I recommend you get another normal system for using Windows if you need to use Windows and keep your Chromebook running ChromeOS for normal tasks you do not require Windows for; you can also remotely connect to the Windows machine from your Chromebook with the aid of an extension.
Unless you really need to use Windows, I recommend against using it. If ChromeOS is capable of doing what you need to do (e.g. web-browsing and online banking, some document editing (you can use Google Docs), listening to some online music) then it should be sufficient.
Stay cautious of malicious Android applications, rogue Google Chrome extensions and online phishing attacks though - those attack vectors will still be present.