How to get highlighting to "stick"?

I was happy to discover that I could highlight words and phrases in a PDF text file. Very cool. But when I drag the file to my desktop (to make a copy outside of DEVONthink), the highlights are gone.

Is there no way to make changes to a pdf in DT “stick” for the purposes of exporting to outside DT?

Yes — press Command-S to Save the edit changes before exporting the PDF.

Hmmm… I got an error when I did that. I wonder if DT saved the changes when I last exited the program? In any case, it now retains the changes when I drag to the desktop. Thanks!