Problems saving and editing tax documents with Adobe Acrobat Reader DC

In previous years, when we would download a 1040 Form from the IRS, we could save it in Adobe and then recall it and come back and edit it.  That is no longer the case.  We have Adobe Acrobat Reader DC, and when we try to go back and edit it says "This document enabled extended features in Adobe Acrobat Reader.  The document has been changed since it was created and the use of extended features is no longer available.  Please contact the author for the original version of this document."

What does this mean and how do I fix it?  We need to be able to call up tax documents, save them partially filled out, and go back and edit them.  This is the first year we cannot do this on any of our computers.  Please help.