When a drawing is on screen you can use wheel on the mouse to scroll and Zoom in and out of the drawing. Pressing and holding the wheel will let you move and pan around the drawing.
Using the keyboard:
Pressing the + key zooms in on the drawing and pressing the ‐ key zooms out.
Pressing the arrow keys (←, →, ↑, ↓) allows panning in the drawing (left, right, up, down).