Somehow I have managed to resize the DevonThink Pro Office on my MacBook Air so large that is extends to all four sides of the screen and I can not click into any corner or side to resize it so that part of the desktop is visible! 
Can anyone out there suggest another way to resize the window please? Many thanks in advance.
If you are in full screen mode the effect is the same. Move the pointer to the upper left corner if your monitor. Don’t click until the red-yellow-green “stoplight” buttons appear. Click the green button to exit full screen mode.
You should also be able to hover over the dock, right click the DEVONthink icon, and choose close all windows.