Markup is a nifty iPhone feature that allows users to doodle, magnify, and add text to images and PDFs in the Photos, Mail, Notes, Files, and Messages apps. Whether you need to add a signature, insert text, or draw shapes onto existing documents or photos, Markup has you covered. With Markup, you can save time when signing digital documents and add your personal flair to your images. Here how to use the markup tools on your iPhone.