Comments not working in online PDF files

I am having this same issue as well.  Only the pin and draw tool are available (which are the two worse tools in the bunch). 

@angelicloud  Thanks for the screenshot as it helps to solve the issue. The message "Unmapped comments" in the screenshot tells us nothing is selected or clicking on a text will give this message. When you use the "Add a comment" box without first clicking on text or an area of the PDF, the comment is "unmapped"—it doesn't have an anchor point on the document. To successfully "pin" a comment to a specific spot, you need to use one of the markup tools first, which automatically anchor the comment to the PDF. The basic comment box you are seeing is for general discussion or text-based markups. Go ahead and click on a location on the PDF to place a sticky note or select text to apply a text markup (like highlight or strikethrough) before typing in the "Add a comment" box to ensure the comment is anchored.