Markup and highlight PDFs on IPad

I have just subscribed to Acrobat on my Microsfot Surface.

I want to be able to review, edit and in particular comment and highlight PDFs. I understood that the ebility to edit documents was included in the subscription i purchased for Acrobat, but I just cannot make it work. The only "edit" option i get requires to me select an element first.

I just cannot make it work. Can someone point me in the right direction?