These let you add comments to PDFs, rearrange pages, add shapes and arrows to call out things in the document, and insert new text blocks and images into the PDF. Then there are PDF annotation apps, including macOS Preview, Xodo, and most mobile PDF apps. They're built to help you read PDF files like you would a book, and help you flip to the page you want, search through the book, highlight text, and perhaps fill out PDF forms and sign them digitally. The PDF apps you've likely used the most-Adobe Reader, Apple iBooks, Windows Reader-are PDF reader apps.
→ Want to make a PDF instead? Check our Guide to Making PDF documents to find out how to build your own PDF documents on any device.
