This is a multi-part article looking into how PDF/X paved the way for future PDF standardization and how the PDF/X family of standards revolutionized the graphics art industry.
Part I: It started with PostScript
Part II: PDF tames PostScript and publishing
Part III: The continued development of PDF/X standards
Part IV: PDF/X in retrospect
The rapid acceptance and adoption of PDF/X-1a for reliable, successful publishing workflows in conjunction with rapidly advancing technological advancement in parallel with changes in the nature of print itself fueled the requirement for newer, more advanced PDF/X standards.
Clearly, the PDF/X-1a from 2001 could not readily meet the needs of the ever-changing print publishing marketplace.
ISO TC 130, WG 2, TF 2 continued to develop new “levels” (versions) of PDF/X between 2002 and 2020. It is not the purpose of this series of articles to exhaustively cover the features of all these new PDF/X versions, but rather, to provide an overview of same. A simple table contrasting the most important of these versions follow these overviews.
Based on Adobe PDF 1.3, PDF/X-3:2002 (ISO 15930-3:2002) added support for ICC color management for objects within the PDF file, not just the Output Intent. Supporting complete blind exchange, this PDF/X version is supported by major graphic arts applications and RIPs, experiencing some limited uptake in Europe. However, it had very little acceptance elsewhere (especially in North America).
Based on Adobe PDF 1.4, PDF/X-1a:2003 (ISO 15930-4:2003) was a technical revision of but substantially the same as PDF/X-1a:2001. There was no PDF/X-1 type of support. No new features were inherited from use of PDF 1.4. Although supported by major graphic arts applications and RIPs, this PDF/X version was effectively ignored by the graphics arts and print communities.
Based on Adobe PDF 1.4, PDF/X-3:2003 (ISO 15930-6:2003) was a technical revision of but substantially the same as PDF/X-3:2002. No new features were inherited from the use of PDF 1.4. Although supported by major graphic arts applications and RIPs, this PDF/X version was effectively ignored by the graphics arts and print communities.
Based on Adobe PDF 1.6, PDF/X-4:2008 (ISO 15930-7:2008) and its update PDF/X-4:2010 (ISO 15930-7:2010) includes the color support provided by PDF/X-3 and added additional features of PDF 1.6 including limited support for layers (Optional Content Groups) as well as compressed object streams and some JPEG 2000 image compression support. It is currently the most appropriate PDF/X for content with any transparency effects.
The PDF/X-4 conformance level provides for complete blind exchange and is supported by major graphic arts applications and RIPs. Carefully created and with some limitations, PDF/X-4 files can concurrently comply and be tagged as compliant PDF/A-2 files for archiving. Although use of PDF/X-4 is disappointingly low, its use has been slowly increasing over the last several years.
The PDF/X-4p conformance level differs from PDF/X-4 in that it provides for externally-referenced Output Intents, thus not providing for complete blind exchange. Although supported by many RIPs, there is absolutely no support for PDF/X-4p in any major graphic arts applications. Its use appears to be limited to some custom applications and systems concerned with the relative size of embedded Output Intents within large collections of small PDF files.
Based on Adobe PDF 1.6, PDF/X-5:2008 (ISO 15930-8:2008) and its update PDF/X-5:2010 (ISO 15930-8:2010) are essentially special-purpose versions of PDF/X-4 supporting the same general features as PDF/X-4. None of the three conformance levels provide for complete blind exchange.
The PDF/X-5g conformance level provides external reference of content via the Reference XObject feature of PDF.
The PDF/X-5pg conformance level extends the functionality of PDF/X-5g by also allowing for externally-referenced Output Intents.
The PDF/X-5n conformance level is similar to PDF/X-4p with the exception that the externally-referenced Output Intent profile is an n-colorant ICC profiles conforming to ISO 15076-1.
At this point, there are no known major graphic arts applications supporting any of the PDF/X-5 conformance levels. There is some RIP/DFE support for PDF/X-5g and PDF/X-5pg (as part of such RIP/DFEs’ support of the PDF/VT-2 standard).
Based on ISO 32000-2:2020 PDF 2.0, PDF/X-6:2020 (ISO 15930-9:2020) extends the graphics support of PDF/X-4 to include a wide range of PDF 2.0 features including but not limited to support for Black Point Compensation, per page Output Intents (with optional CxF/X-4 spectral data), and Document Part metadata. Use of annotations within the visible area of a page as well as non-XFA forms, digital signatures, and some Actions are now allowed with some notable restrictions.
The PDF/X-6 conformance level provides for complete blind exchange. Carefully created and with some limitations, PDF/X-6 files can concurrently comply and be tagged as compliant PDF/A-4 files for archiving. The PDF/X-6 and PDF/A-4 standards were developed concurrently and care was taken in the standards development to ensure this commonality.
The PDF/X-6p conformance level differs from PDF/X-6 in that it provides for externally-referenced Output Intents, thus not providing for complete blind exchange.
The PDF/X-6n conformance level is similar to PDF/X-6p with the exception that the externally-referenced Output Intent profile is an n-colorant ICC profiles conforming to ISO 15076-1. Likewise, it does not provide for complete blind exchange.
Given that we are currently only one year out from publication of the PDF/X-6 standard, there are not yet any known major graphics applications supporting any of the PDF/X-6 conformance levels. The expectation / hope is that such support will be forthcoming within the coming year. Stay tuned!
There was one PDF/X standard that is not referenced above or in the comparison table below. That standard is or maybe better expressed as was PDF/X-2:2003 (ISO 15930-5:2003). Withdrawn not long after its publication, PDF/X-2 supported a form of OPI using Reference XObjects to access external content but also supported color in a manner similar to PDF/X-3. There are no known applications that supported PDF/X-2.
The PDF/X-6 standard was developed to best support the future, complex PDF print publishing workflows from content design to rendering and finishing as well as continue to support current simpler workflows. However, due to the fact is that it will probably be a year or more before we see any support for PDF/X-6 creation in any major graphics applications, the recommendation is to use the PDF/X-4 standard which has quite robust support in all major graphics applications as well as RIPs / DFEs.
The “newer” PDF/X standards, beginning with PDF/X-4, provided the base for additional ISO standards supporting variable and transactional publishing and printing (VDP).
The PDF/VT standards ISO 16612-2:2010 Graphic technology — Variable data exchange — Part 2: Using PDF/X-4 and PDF/X-5 (PDF/VT-1 and PDF/VT-2) and ISO 16612-3:2020 Graphic technology — Variable data exchange — Part 3: Using PDF/X-6 (PDF/VT-3) define standards by which PDF files may be optimized in terms of size, performance, and operations for variable and transactional publishing and printing.
In the case of PDF/VT-1 conformance level, supporting complete blind exchange, the PDF files comply with the specification for and are tagged as PDF/X-4 files in addition to complying with and being tagged simultaneously as PDF/VT-1 files.
For the PDF/VT-2 conformance level supporting external content (i.e., not complete blind exchange), the PDF files comply with the specification for, and are tagged as, PDF/X-4, PDF/X-4p, PDF/X-5g, and PDF/X-5pg in addition to complying with and being tagged simultaneously as PDF/VT-2 files.
The PDF/VT-2 conformance level supports a MIME package of one or more PDF/VT-1 and/or PDF/VT-2 “chunks” each of which conforms to their respective PDF/VT conformance level.
For the PDF/VT-3 conformance level, supporting complete blind exchange, the PDF files comply with the specification for and are tagged as PDF/X-6 files in addition to complying with and being tagged simultaneously as PDF/VT-3 files.
Prior to the publication of the initial PDF/VT standards, VDP was supported by any number of non-PDF-based protocols, some of which were standardized (such as PPML) and others of which were proprietary to a particular printer vendor. These protocols were most often based to some degree on an underlying PostScript renderer and were not appropriate for the current era of pure PDF RIPs and DFEs.
Twenty Years of PDF/X continues with PDF/X in Retrospect.
For over 31 years, Dov Isaacs was a Principal Scientist at Adobe, Inc. with responsibility for end-to-end PDF publishing workflow and product interoperability issues. Dov also served as Adobe’s representative to several ISO TC130 committees associated with print industry standards including PDF/X and PDF/VT for which he serves as the chairperson and co-chairperson respectively. He monitors numerous InDesign, PDF, prepress, and …