Sometimes when trying to edit or specifically change the color of text in an existing pdf, I get an error message saying "this document restricts some features of Adobe Acrobat DC..." and asks me to save a copy. That doesn't work either. We previously owned a copy of Adobe Acrobat Pro, but replaced it with the cloud version. I never had this problem before, and my job requires occasional font color changes of some items in a pdf form.
When it says to save a copy you have to do it via File - Save A Copy, not just to make a copy of the file, if that's what you're doing.