how can I connect two objects from diffrent windows in qt?

I have a window1 which has 2 buttons, one "add" button and a "next" button. The "add" button is initially disabled. Once clicked on "next" button, a new window2 is opened. On that window there is a "OK" button. What I wanna do is enabling the "add" button from window1 after clicking on the "OK" button from window2. Is it possible to connect two objects ( signal & slot ) from diffrent windows ? If it is the case, where ( on which .cpp file ) do I have to write the connect function ?