Shorcut to pan in Preview?
You can use your mousewheel to pan up and down. Use Shift + mouse-wheel to pan left and right.

I just found that it may be easier to use Quick Look for the feature you're after. In finder, select your file and press the Spacebar to open it in Quick Look. Then if you use command+ you can zoom in.  Then you can click and drag to pan.

Use command- to zoom out, and Spacebar or esc to exit.