I start a file in Illustrator with these settings:
I save the file with these settings (no PDF compatible file):
The AI file weighs 1.1 MB.
I place a JPG picture from a DSLR camera which weighs 4.4 MB, rescaled to A4 size. I save it and it still weighs 1.1 MB.
I save it as PDF with the standard settings, except that I uncheck "Keep Illustrator editing capabilities":
The PDF now weighs 33.1 MB.
I would expect the PDF file to simply embed the JPG image with coordinates and thus be only be marginally larger than the photo, or maybe a bit more for thumbnails. Instead, the PDF is more than 7 times larger than the original.
Why is the PDF so large?