Make sure you are opening the PDF in Acrobat Standard DC to edit the PDF files not in Acrobat Reader DC.
Acrobat Standard DC & Acrobat Reader DC are two different application.
Acrobat Standard DC is PDF creator/editor & Acrobat Reader DC is a PDF viewer.
You cannot edit PDF files using Acrobat Reader DC.
I am using Acrobat Standard DC. It gives me this message when I try to open it, “This feature is not included in your acrobat license.”