How to Highlight, Underline & Strikethrough Text 1. Open a PDF file you’d like to add markups to. 2. Click on the markup tools and select the colors you like. 3. You may change the markup anytime by right-clicking (or "control" + click) and selecting your changes. Have more questions? Submit a request 2 Comments Date Votes 0 Praveen Rao May 23, 2020 02:20 how to undo text underline or highlight. Unable to undo. I am using Mac OS Catalina. Thank you Praveen Rao 0 Gina June 18, 2020 01:00 Hello Praveen, If you wan to use the undo/redo function. Please try to use Edit > Undo/Redo from the top menu. If you still have concerns, please contact us at email@example.com . Thank you :) Please sign in to leave a comment.