Click the Create New Rectangle tool or the Create New Ellipse tool.
Position the pointer on a page
of the PDF document and do one of the following:
To draw a new rectangle or ellipse, drag
diagonally.
To draw a square or circle, hold down
the SHIFT key
while dragging.
To draw a rectangle or ellipse, starting
from its center and not from its side, hold down the ALT key (Windows)
or Option key
(Macintosh) while dragging.
Drawing from side keeps the sides of the
shape in a fixed position along the x and y axis
Drawing from center
keeps the center point in a fixed position.
To draw a square
or circle, starting from its center, hold down both the SHIFT key and
the ALT key
(Windows) or Option key
(Macintosh) while dragging.