The printing conditions or output intent need to be specified in the file. This can be specified in the form of standard profiles using codes, like "CGATS TR 001 SWOP".
In the PDF/X file each graphic gets its own color profile, so even though the file as a whole is CMYK, individual graphics may be RGB (with calibration information).
Active content is
not allowed in a
PDF/X file. This
means that standard
PDF features like
embedded sounds and
movies are not
allowed in PDF/X.
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