PDF/X
PDF/X is a subset of the ISO standard for PDF. The purpose of PDF/X is to facilitate graphics exchange, and it therefore has a series of printing-related requirements which do not apply to standard PDF files. For example, in PDF/X-1a all fonts need to be embedded and all images need to be CMYK or spot colors. PDF/X-3 accepts calibrated RGB and CIELAB colors, while retaining most of the other restrictions of PDF/X-1a.
PDF/X files must not only follow certain restrictions, they also must contain a special file identification, inside the PDF, which says which PDF/X version they are. This means that a file can only conform to a single specific PDF/X standard, even if all other requirements of another version are met.
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 a PDF/X file that has color-managed data, each color-managed graphic gets its own color profile, so even though the file as a whole is CMYK, individual graphics may be RGB.
Various boxes must be defined: the MediaBox, which defines the size of the entire document, and either the ArtBox or the TrimBox, which defines the extent of the printable area. If the file is to be printed with bleed, a BleedBox, which must be larger than the TrimBox/ArtBox, but smaller than the MediaBox, must be defined.
Active content is not allowed in a PDF/X file. This means that standard PDF features like forms, signatures, comments and embedded sounds and movies are not allowed in PDF/X. Features that are forbidden in the PDF/X standard can sometimes be used, if they do not affect the rendering of the file. This allows for things like annotations outside the BleedBox.
List of the PDF/X standards
PDF/X is formalized in ISO standards 15929 and 15930:- ISO 15929 specified the guidelines and principles for the development of PDF/X standards.
- ISO 15930 defines the specific implementations:
- * : PDF/X-1a:2001, blind exchange in CMYK + spot colors, based on PDF 1.3
- * ISO 15930-2: PDF/X-2, was never published.
- * : PDF/X-3:2002, allows CMYK, spot, calibrated RGB, CIELAB, with ICC Profile, based on PDF 1.3.
- * : PDF/X-1a:2003, revision of PDF/X-1a:2001 based on PDF 1.4
- * : PDF/X-2, An extension of PDF/X-3 which allows for OPI-like data to be included. It was withdrawn in 2011.
- * : PDF/X-3:2003, revision of PDF/X-3:2002 based on PDF 1.4
- * : PDF/X-4, Colour-managed, CMYK, gray, RGB or spot color data are supported, as are PDF transparency and optional content. A second conformance level named PDF/X-4p may be used when the ICC Profile in the output intent is externally supplied. It is using PDF 1.6. A second edition with minor corrections and improvements is .
- * : PDF/X-5, with a second edition with minor corrections and improvements as . It is based on PDF 1.6. A collection of three conformance levels:
- ** PDF/X-5g: An extension of PDF/X-4 that enables the use of external graphical content. This can be described as OPI-like workflows. Specifically, this allows graphics to be referenced that are outside the PDF, which "can have value in reducing... demands... by allowing... work with low resolution" .
- ** PDF/X-5pg: An extension of PDF/X-4p that enables the use of external graphical content in conjunction with a reference to an external ICC Profile for the output intent.
- ** PDF/X-5n: An extension of PDF/X-4p that allows the externally supplied ICC Profile for the output intent to use a color space other than Grayscale, RGB and CMYK.
- * : PDF/X-6 based on PDF 2.0 and was published in November 2020. It defines the extensions PDF/X-6p and PDF/X-6n for partial exchange of printing data with external profile reference.