Rectangular.
Tools panel "rectangle" button.
Move the cursor over the document window.
The cursor changes to a ┼.
Dragging the mouse.
Determine the size and shape of the rectangle.
It will become a square if a mouse drug is started pressing the option key.
Release the mouse button.
Fix a rectangle.
It will become a rectangle, if it resizes using the knob of four corners after starting a mouse drug, pressing the option key. A square will be maintained if it resizes using a middle knob.