Edit paths with the Pencil tool

You can edit any path using the Pencil tool and add freeform lines and shapes to any shape.

Select an existing path.
Select the Pencil tool.
Position the pencil tip on an endpoint of the path.
You can tell you’re close enough to the endpoint when the small x next to the pencil tip disappears.
Drag to continue the path.

Select both paths (Shift-click or drag around the two with the Selection tool).
Select the Pencil tool.
Position the pointer where you want to begin from one path, and start dragging toward the other path.
After you begin dragging, hold down Ctrl (Windows) or Command (Mac OS). The Pencil tool displays a small merge symbol to indicate you’re adding to the existing path.
Drag onto the endpoint of the other path, release the mouse button, and then release the Ctrl or Command key.
Note: For best results, drag from one path to the other as if you were simply continuing the paths in the direction they were created.

Select the path you want to change.
Position the Pencil tool on or near the path to redraw.
You can tell you’re close enough to the path when the small x disappears from the tool.
Drag the tool until the path is the desired shape.
Using the Pencil tool to edit a closed shape

Note: Depending on where you begin to redraw the path and in which direction you drag, you may get unexpected results. For example, you may unintentionally change a closed path to an open path, change an open path to a closed path, or lose a portion of a shape.

Illustrator