Commenting tools are available only in
PDFs that have commenting enabled. PDFs in a review workflow typically
include commenting rights. You use commenting and markup tools (View > Toolbars > Comment & Markup) to add comments. Comments are notes and drawings that communicate ideas or provide feedback for PDFs. You can type a text message using the Sticky Note tool, or you can use a drawing tool to add a line, circle, or other shape and then type a message in the associated pop-up note. Text-editing tools let you add editing marks to indicate changes you want in the source document. Most commenting and markup tools don’t appear in the toolbar until you add them.
Most comments include two parts: the icon, or markup, that appears on the page, and the text message that appears in a pop-up note when you click or double-click the icon or place the pointer over the icon.
After you add a comment, it stays selected until you click elsewhere on the page. A selected comment is highlighted by a blue halo to help you find the markup on the page. A wireframe with selection handles appears so you can adjust the size and shape.

Show the Comment & Markup toolbarThe Comment & Markup toolbar doesn’t appear by default, except when you open a PDF in a managed review workflow.
Do one of the following:Choose View > Toolbars > Comment & Markup.
Choose Tools > Comment & Markup > Show Comment & Markup Toolbar.
Click the Review & Comment button
in
the Task toolbar, and choose Show Comment & Markup Toolbar.
To add or remove tools for this toolbar,
right-click/Control-click the toolbar, and select the tool. Or,
choose Tools > Customize Toolbars.
Select a commenting or markup tool
Do one of the following: Select a tool from the Comment & Markup toolbar.
Choose Tools > Comment & Markup > [tool].
Keep a commenting tool selected