Could you let us know the device you are having this issue on? Is it an Android phone/tablet, iPhone/iPad or a Windows touch device? What is the Adobe Acrobat version installed on the device?
We would require some additional details about the issue so that we may investigate the same:
Adobe Acrobat Team
I have a Kindle Fire. Adobe Acrobat DC. The problem occurs only during the time I try to highlight lines In a book I have downloaded. I have always use the highlight pen at the bottom of the page but now I get a message saying I have to pay for this now. However, I have found another way to highlight I just hold the first letter in the line I want to highlight, drag the blue ball across the page from left to right, click highlight and it's done. So it's all good now.