This article show three methods that can be used to add audio comments to PDF documents in Adobe Acrobat free and Pro version.

Need to edit a PDF document but don’t want to pay for the more expensive Adobe editors? You can add text to and sign a PDF with just the free Reader program.

It's not immediately obvious, but when viewing PDF documents in the Files app, there are hidden tools that enable you to rotate pages, add blank pages, insert images, delete pages, and even scan ...