PDFs are great, portable, cross-platform documents that you can read on your Mac, your iPad or iPhone, or on a PC. But this ubiquitous file format is also useful when you need to share works in progress with your colleagues. You don’t need to buy an expensive program to add comments or notes to a PDF. Distribute a PDF document for comments, get back the annotated files, and make changes in your original—all using Apple’s free application, Preview (in your /Applications folder).

Turn on annotations

To start with, open a PDF in Preview, and then click on the toolbar button that looks like a pencil. (You can also choose View -> Show Annotations Toolbar or press Command-Shift-A.) This displays the annotation toolbar, which contains a dozen buttons that let you access a variety of annotation features.

Activate any of these features by clicking its button; you can also activate each of them from the Tools -> Annotate menu, where you will see keyboard shortcuts for each tool as well. You might want to commit to memory those which you use frequently.

Highlight text

Highlighting text is an easy way to mark sections you want to remember, or to mark parts of a text you want to point out to others. To highlight text, click the second button in the annotation toolbar—the one that looks like the tip of a highlighter—then select the text you want to highlight. (Or, press Command-Control-H.) Click and drag the cursor to highlight long sections of text. Double-click to highlight a word. Triple-click to highlight a full line. If you mistakenly highlight something and want to undo it, just press Command-Z.

Add notes

After you’ve highlighted something in a PDF, you may want to add a note to explain why you’ve highlighted it or to offer a proposal for a change. To do this, click the notepad button in the annotations toolbar (or press Command-Control-N). The content of your PDF will slide to the right, and a gray sidebar will appear to the left; this is where the texts of your notes will go.

Your cursor is now a crosshair; click it where you want to place your note. A yellow section will appear in the sidebar, with your name and the date. (You can choose to not display your name; go to Preview -> Preferences -> PDF and uncheck Add Name to Annotations.) Start typing to replace the selected text, or move your cursor to the end of the yellow box to retain it. Add any comments you wish.

You can move notes; just click on a note icon and move it where you want. To delete a note, click on the icon to select it, then press the Delete key. Hide note texts by clicking the x icons in their yellow boxes; click on a note icon on the PDF again to display the text.

Choose From More Annotation Options

Preview’s other annotation features let you add rectangles, ovals, lines, and arrows to highlight different sections of your documents. You can strike through or underline text. You can even add text boxes, speech boxes and thought bubbles.Most of these annotations transfer correctly to the free Adobe Reader X and $800 Adobe Acrobat X Pro. Try out the different options, and you’ll find that these annotation features make Preview a great tool for marking up documents and collaborating with others.

Senior contributor Kirk McElhearn writes about more than just Macs on his blog Kirkville. Twitter: @mcelhearn Kirk is the author of Take Control of Scrivener 2.