Thanks for your reply guys. Offering the StudioLink I hoped to avoid CMYK conversion and Adjustment Layer changes on the reference picture before importing it into Publisher...
As you said: > The PDF exporting process is first converting the RGB document to CMYK and then compositing and exporting.
For comparison of the different export routes I also tried to export the same document to JPG considering the conversion into sRGB and CMYK. The results are much more similar than the PDF export.
It seems, that in the case of JPG export, Publisher applies the Adjustment Layers onto the RGB picture before converting into CMYK. In case of PDF export the RGB picture is converted into CMYK first, and afterwards applying the Adjustment Layers. In contrast the preview and softproof inside of Publisher always considers the layers from bottom to top and in my case adds the CMYK softproof conversion at the end.
So wouldn‘t it make sense to apply the same processing route for all export formats and the preview inside of Affinity Publisher?