Hosting external application on UI element

We are developing an application on Unity with VR. In our application we need to open an external app (ex. Notpad) and interact with the app. The external app needs to be opened ON the UI, not on external normal windows' window. The approach should be (as we think) by getting the app handle and pass it to a unity UI element (ex. a UI panel)

Hope you can help us with that.

Thanks.