PDF Expert: a robust annotation tool for Mac desktops, iPads and iPhones. Offering a multitude of annotation options (highlighter, stamps, text, note, underline, shape, etc) on a wide range of files (PDF, document, spreadsheet, image, video, audio, etc). Offers seamless synchronization with cloud storage platforms such as DropBox and Box, and a Markup feature for PDF files with powerful editing abilities. Paid.