Adobe Acrobat X Pro versus Adobe Acrobat Pro DC

Prior to our upgrade to Pro DC we were using X Pro and even after a digital signature was applied to the document, I was still able to add a text box to add a few other details.

In DC, when you try to add a text box to a PDF file, you get the message “This file is signed, and cannot be edited”. So I downloaded it to my home computer, and did *exactly that* in Adobe Acrobat X Pro and was able to do so without any issues. Why does DC fail here where X Pro does just fine?

What would be the new way of accomplishing this in Pro DC.