I'm using Scribus 1.5.8; in the "Save as PDF" dialog (General tab), the "Embed PDF & EPS files (EXPERIMENTAL)" option and its check-box seem to be permanently greyed out.
Using Scribus 1.5.5 a couple of years ago I wrote an 92-page training manual with 35 detailed PDF diagrams which I'd drawn in Inkscape, many of which include raster elements (blurring or opacity-gradients). I added these PDF files to my Scribus document within Image Frames. In Scribus 1.5.5 this all exported fine, with every part of my lovingly crafted PDF diagrams faithfully reproduced in the final document, and the text in the diagrams searchable too.
My folder even contained a note to myself to use ONLY Scribus 1.5.5 because it was the last version where this "Embed PDF" option worked. However, today when I came to update my book, I found that 1.5.5 always crashed on load because (I think) Python 2.7 is no longer included on my Mac (nor does it seem to be possible to insert a symlink to a version I could install using MacPorts).
I've tried inserting the PDF file directly into the Scribus document, but this loses the raster elements I described, prevents text-searching, and possibly does something nasty to the colours too.
Any ideas, please?