Using the Pen Tool (P), draw a shape like the red one (shown below) that covers the top corner of the rectangle shape. Select the red shape and the gray rectangle and in the Pathfinder select Subtract from Shape Area followed by clicking Expand.Using the Pen Tool (P), draw a shape like the red one (shown below) that covers the top corner of the rectangle shape. Select the red shape and the gray rectangle and in the Pathfinder select Subtract from Shape Area followed by clicking Expand.