I am attaching a set of four screen shots with captions. The first screen shot shows how HP Smart does this correctly for my HP 6978. The next three screen shows show the attempt to do it with Acrobat Pro DC, where the actual interface does not match what the above link says should happen.
An undesirable workaround is to just duplex scan and save with HP Smart, which produces just the page images and a huge file. Then use Acrobat to read that file, search for some text to force it to do image to text conversion, then save the file back to itself with "Reduce File Size." However this workaround does not allow any of the custom settings available when using Acrobat for the original scan as shown in image 2 (which clearly requests scanning both sides, but ends up in image 4 asking if done or go back to scan reverse).
Please provide a solution that actually works for the HP 6978. Thanks.