1. Ensure the Commenting toolbar is visible (View > Toolbars > Commenting).
  2. Click the Stamp tool in the toolbar.
  3. Click anywhere on a page to add a stamp of default size or click+drag to create a stamp of a custom size.
  4. To choose a different stamp:
    1. Click and hold the black triangle on the Stamp tool to reveal the menu of available stamps.
    2. Choose Built In to see the selection of pre-defined stamps.
  5. Double-click a stamp placed in your document to open its associated note window.