I think it's weird if this happens with ALL pdfs you produce. Could it be that you have a less-than-ideally-optimized logo or something on your master layouts?
Anyway, I find AC12's pdfs are often better than AC11's. If you have bitmapped images (photos, scanned maps etc) you should if possible insert them as high-quality jpgs instead of tiffs, and turn off transparency if possible. If you have inserted PDFs, note that they may contain images like the above that may be problematic.
Sometimes it helps to open Archicad's output pdf through Adobe Acrobat (full commercial version). In the
File menu, there is a
Shrink File (or similar) command that may help. It optimizes the pdf.
AC4.1-AC26SWE; MacOS13.5.1; MP5,1+MBP16,1