The Nitro Pro text mark-up tools let you work with a PDF file as if it were a printed on paper, and you can undo and redo a modification should you wish to correct a mistake.
An annotation comment is a non-destructive element, which is added as an extra layer over the page of your PDF, and can be removed at any time. If you want comments to appear when you print your document, you have to specifically enable annotations in your print settings.
You can add comments to pages as sticky notes, text highlighting, drawing markups, stamps, and file attachments.
Most types of comments include a pop-up note, enabling you to add additional feedback. For example, if you’ve marked some text with the Highlight Text tool, you can open the corresponding pop-up note and type an explanation to clarify why you’ve highlighted it. You can also use the Comments pane to view, manage and organize comments from others.
All commenting and drawing tools are accessible from the Review tab.
For more information about comments and annotations in PDF files, see: