'Generating PDF' of a pdf. Why?

Anyone know why this keeps randomly appearing and how to make it stop.

The file is already a pdf so what is it generating? ...and why is it downloading images? ...and to where?

It's almost impossible to search for an answer or any kind of help because the message is so vague and generic. I've ajdusted/disabled some settings in accessibility, Multimedia, Page Display, etc., but DC's redraw/preview is still infuriatinly slow (even stalls completely), and this window just adds to the annoyance.

Any help would be greatly appreciated.

Thanks!