Assuming the obvious way is unavailable because the header of the window is out of range and there's no where to grab it. (BTW- I don't know why apple changed this. there used to be a frame around the entire window that was grab-able)
Anyway,- this sometimes happens if you change the screen resolution while PT is running. Usuallly restarting the computer will resize everything happily, or at least it will move the header of the window into view so that you can move it around to bring the resize corner into view.

In the upper left side of the window hit the greeen button with the "+" to fit window to screen.

8)

gdoubleyou wrote: In the upper left side of the window hit the greeen button with the "+" to fit window to screen.

8)

You get the gold star!

Thanks

wow, in that case, you're right- it is the Dumbest problem ever.
I always assume that people post questions because the normal accepted procedure didn't work and using the search function didn't produce any results.
But yeah and for future reference:
Red button - closes
Yellow button - sends to the Dock
Green Button - toggles current view/fits window to screen.
These are all very well documented controls.

I liked the more technical answer with the restart.