Quote:...I do not know whether this is a GIMP, export settings, or ICC issue, and if anyone can recommend a solution, workaround or use of another programme to succeed, I would appreciate it greatly.
Another day, another look at what might work.
You can use Gimp to export your image with the romm icc profile and check using ImageMagick https://imagemagick.org command line as:
Adobe says that PDF/X-4 keeps the RGB image profile even though the "rest" is cmyk
The best freeware tool for PDF publishing is Scribus https://www.scribus.net/ and a RGB image looks like this.
When it comes to export PDF/X-4 for printing, all the options are greyed out (that is usual) You set up profiles etc in preferences, but the RGB image profile shows.
So far I have not found a utility that confirms that the PDF does use that specific icc profile.