Preview is an incredibly powerful tool, and it’ll only get more powerful in macOS Mojave. Beyond letting you, well, preview PDFs and images, Preview allows for a ton of annotations for PDF that are compatible with Adobe’s PDF app, Acrobat, which is used by Windows users and companies, making it easy to share annotated documents with colleagues, regardless of the platform they use.
Make sure the Edit Toolbar is visible (from the View menu) and you'll see you've got options for drawing shapes, arrows, speech and thought bubbles and more.
Make sure the Edit Toolbar is visible (from the View menu) and you'll see you've got options for drawing shapes, arrows, speech and thought bubbles and more.
There's also the option to highlight text in different colours, strikethrough some text, add notes and type some text into boxes.