I assume you mean the Xara PDF Editor in Designer Pro.
This is aprogram for editing and converting files to PDF format which is the most common document format for sharing on the Internet.
AFAICS there is very little information about it on the Magix and Xara websites, if it is not mentiioned in the Designer Pro manual or under Help in the program - the closest information is the Xara Cloud version here.
I believe that the PDF Editor 4 is part of Xara, not something separate or a separate program. You simply open or drag the pdf into Xara DPX and edit. What you are seeing are the new features that are part of the pdf editor within Xara.