German term (edited): in Form einer verrechneten Bild-PDF Datei

The source text seems a bit wordy. "Verrechnen" or "rechnen" describes the process of converting a file to PDF. However, since all PDF files are by nature "converted," it's not really necessary to specify that you need a "converted PDF file." Apparently the supplier just wants to emphasize that they do not want to receive the proof as a Postscript file or as original files (nooo!) that they would have to convert themselves (with the potential risks, besides the additional pre-press fees for the customer); the supplier just wants the data converted and delivered as a printable PDF.

You'll find some examples when searching "PDF rechnen" and "PDF verrechnen."

"Bild-PDF" isn't a commonly-used term, either. A PDF file used for printing folding boxes obviously will contain an image, but it doesn't need to be called an "image PDF." And a "Korrekturabzug" (proof) is normally provided by the printer TO the customer--not the other way around; but it's pretty clear they are referring to the version with the customer's changes implemented.

So I would just suggest something like, "Changes/corrections are to be delivered as (or in the form of) a PDF file."