Forensics: electrostatic detection circuit for lifting "indentations" from documents
Anyway, to answer the actual question, a couple of thoughts pop to mind. First of all, to correct a misconception, the EDD process measures the charge left on the film after it has been in contact with the paper "for a few minutes". The paper itself does not retain a charge.

The Versatec printer was an early electrostatic printer/plotter that used an array of "nibs" to write an electric charge pattern directly onto paper, which was then developed using toner suspended in liquid (rather messy, unfortunately). The same nib array could conceivably be used to sense electrostatic patterns on plastic films.