PDFX-ready is a Swiss initiative founded in 2005. The goal is to promote and facilitate the use of the PDF/X ISO Standards for the exchange of printing data.
PDFX-ready creates guidelines, instruction sheets (called recipies), application settings (colour, pdf export) and preflight profiles. The PDFX-ready specifications are based on the PDF/X-Plus specifications of the Ghent (PDF) Workgroup.
PDFX-ready guide – Version PDF / X-4 CMYK
More information can be found on the website of PDFX-ready.