When I use the Tools > Certificates > Digitally Sign method the Digitally Sign Method is greyed out.
There are grey boxes in my pdf but when I click them nothing happens too.
I hope you are doing well. I am sorry for your experience with Acrobat Reader.
Are you experiencing this issue with a single file or all the files? If with a specific file, please share a screenshot of the description page for the document.
To get to the description, click on File-> Properties.
Also, you may refer to the below link, another community thread with an issue similar to yours. Let me know if it helps: