Double-click the Pencil tool  to set any of the following options:

Fidelity

Controls how far you have to move your mouse or stylus before a new anchor point is added to the path. The higher the value, the smoother and less complex the path. The lower the value, the more the curves will match the pointer’s movement, resulting in sharper angles. Fidelity can range from 0.5 to 20 pixels.

Smoothness

Controls the amount of smoothing applied when you use the tool. Smoothness can range from 0% to 100%. The higher the value, the smoother the path. The lower the value, the more anchor points are created, and the more the line’s irregularities are preserved.

Fill New Pencil Strokes

(Illustrator only) Applies a fill to pencil strokes you draw after selecting this option, but not to existing pencil strokes. Remember to select a fill before you draw the pencil strokes.

Keep Selected

Determines whether to keep the path selected after you draw it. This option is selected by default.

Edit Selected Paths

Determines whether or not you can change or merge an existing path when you are within a certain distance of it (specified with the next option).

Within: _ pixels

Determines how close your mouse or stylus must be to an existing path in order to edit the path with the Pencil tool. This option is only available when the Edit Selected Paths option is selected.