Well, you have two problems here.

The first is the easiest to solve: to put tabs within one of your
Forms, just add a TabControl to the form and then add the TabPages you
need to the TabControl's TabPages property. You can do this either at
design time (using Visual Studio designer) or at run time in code. The
easiest way to do the latter is to do it first at design time using the
Designer, and then look at the code it generates and make your code do
the same thing.

The second problem is how to host an independent Windows application
like Notepad or Wordpad inside your own application. I have no idea how
to do that: someone else here will have to help you with that.