Select the desired document. 4. Click on the highlighter in the upper right hand corner of your Adobe Reader screen. You'll see three options on the very right hand side: Tools, Fill and Sign, Comment. To the left of the Tool option you'll see the icon to expand the page.Right next to it you'll find the highlighter.. Click on the highlighter in the upper right hand corner of your Adobe Reader screen. You'll see three options on the very right hand side: Tools, Fill and Sign, Comment. To the left of the Tool option you'll see the icon to expand the page.