The Pencil tool is usually used to draw free-form lines on PDF document pages and the Eraser tool is used to erase parts of the pencil markups that you’ve drawn.

To mark up with the Pencil tool:

1. Choose Comments > Draw Tools > Pencil, or select the Pencil tool in the Comment toolbar.
2. Move the pointer to where you want to begin drawing. You don’t have to use one unbroken stroke. You can release the mouse button briefly, move the pointer to a new location, and continue drawing.

To edit the pencil markup:

1. To change the line thickness, color and opacity, right-click the drawing and select Properties from the context menu. Select the options you want from the Pencil Properties dialog box. See Setting Comment Properties.
2. To erase parts of the drawing, choose Comments > Draw  Tools > Eraser or select the Eraser tool on the Comment toolbar. Then drag across the areas of the drawing you want to remove.

Pencil and Eraser