Illustrator

Trap a portion of an object

  1. Draw a line along the edge or edges that you want to trap. If the object is complex, use the Direct Selection tool  to select the edges to be trapped, copy them, and choose Edit > Paste In Front to paste the copy directly on top of the original.
    Drop shadow with a trap (left) is based on the line drawn where the object and its drop shadow meet (right).

  2. In the Stroke box in the Tools panel or the Color panel, select a color value for the Stroke to create either a spread or a choke.
  3. Choose Window > Attributes.
  4. Select Overprint Stroke.