Comment 21 for bug 574717

This seems to take some time still, so I built a workaround some time ago that I want to share:

This desktop file:
[Desktop Entry]
Hidden=false
Exec=pdf2pdfx
Icon=/usr/share/icons/oxygen/64x64/apps/acroread.png
Type=Application
NoDisplay=true
Version=1.0
MimeType=application/pdf;
StartupNotify=false
GenericName[en_US]=PDF to PDF/X-3 converter
Terminal=false
Name=PDF to PDF/X-3 converter
GenericName=PDF to PDF/X-3 converter
Icon[en_US]=/usr/share/icons/oxygen/64x64/apps/acroread.png
Name[en_US]=PDF to PDF/X-3 converter

which calls
#!/bin/bash

gs \
-dPDFX \
-dBATCH \
-dNOPAUSE \
-dNOOUTERSAVE \
-dPDFSETTINGS=/prepress \
-dCompatibilityLevel=1.5 \
-sDEVICE=pdfwrite \
-sColorConversionStrategy=CMYK \
-sProcessColorModel=DeviceCMYK \
-dHaveTransparency=false \
-sOutputFile="${1%%.pdf}_X-3.pdf" \
PDFX_def.ps \
"$1"

and /usr/share/ghostscript/*/lib/PDFX_def.ps countaining the icc profile you intend to use will make you able to convert any pdf with a few clicks in your file manager. This is PDF/X-3 then, which is what most prepress shops want.
Combined with a color-managed setup in inkscape with the same profile will get you decent color reproducibility.

hope that helps,
th