Apple’s excellent Preview application provides an easy way to work with images and PDFs. Despite its unassuming name, it can be used to edit images and annotate PDFs (though not edit their text). Annotations include notes, links, highlights, arrows, shapes, and text boxes. Adding shapes, like rectangles and ellipses, is useful, but it can often be hard to position them correctly. I recently learned a trick that makes it much easier: just select the text you want to box or circle, and click the button in the annotations toolbar. The new shape is automatically placed around the selected text, though it can then be moved or scaled. And remember than the color and thickness of a shape can be customized in the toolbar.