PDF is a very versatile file format. Unfortunately this also means that it is very easy to create PDF files that are completely useless in a prepress environment. The solution to this problem is to define a set of rules that forbid the use of certain PDF functions that are irrelevant for printing purposes and to enforce others that do improve its usefulness in prepress. This set of rules is called PDF/X, a series of well defined subsets of the PDF standard that promise predictable and consistent PDF files.
PDF/X-3 is one of the more popular PDF/X flavors. This page covers:
- What are PDF/x-3 files?
- Which other PDF/X flavors exist?
- PDF/X is just the starting point
- How to create PDF/X-3 files
What is a PDF/X-3 file?
PDF/X-3 files are regular PDF 1.3 or PDF 1.4 files.
There are a number of restrictions that apply to PDF/X-3 files:
- All fonts must be embedded in the file.
- All color data can be grayscale, CMYK or named spot colors. RGB, LAB or ICC based color spaces are also allowed. If such device-independent colors are used, both the embedded ICC profiles and the Rendering Intent defined in the PDF/X-3 file must be taken into account when it is processed. This means that you need a color management aware workflow (and a color management aware operator) to be able to process PDF/X-3 files.
- OPI is not allowed in PDF/X-3 files.
- PDF/X-3 files cannot contain music, movies or non-printable annotations.
- If there are annotations (sticky notes) in the PDF, they should be located outside the bleed area.
- Only a limited number of compression algorithms are supported.
- Encryption cannot be used.
- Transfer curves cannot be used.
- The use of live transparency is not allowed in PDF 1.4 file.
Next to things that are not allowed, there is also some information that needs to be present in a PDF/X-3 file but that you may not find in regular PDF files:
- Metadata indicate that the PDF file is a PDF/X file and also detail what type of PDF/X file it is.
- There is a separate flag (ON or OFF) that details whether the file has already been trapped.
- PDF/X-3 files contain extra operators that define the bleed and trim area.
- The MediaBox defines the size of the entire document
- The ArtBox or TrimBox defines the extent of the printable area.
- If the file is to be printed with bleed, a BleedBox must be defined. It must be larger than the TrimBox/ArtBox, but smaller than the MediaBox.
- The file needs to contain an ICC color profile which defines the color space of the CMYK data. This profile needs to be embedded as an OutputIntent.
There are 2 different PDF/X-3 flavors:
- PDF/X-3:2002 – such a file has to be a PDF 1.3 file
- PDF/X-3:2003 – such a file has to be a PDF 1.4 file but it should not contain any transparency and JBIG2 compression should not be used to compress images.
Both flavors share all of the restrictions that apply to PDF/X-3. The 2003 version simply came along because some newer software applications no longer supported the older PDF 1.3 file format.
- PDF/X-3 is an official ISO standard: ISO 15930-6.
- An excellent white paper about PDF/X-3 can be found here.
- The PDF/X-3 standard was developed in Germany and Switzerland. Its use also seems to be largely restricted to those countries.
- Some of the early PDF/X-3 adapters quickly learned that color management issues made it difficult for them to adopt a ‘true’ PDF/X-3 workflow. They promoted the use of CMYK in PDF/X-3, essentially ‘downgrading’ to PDF/X-1a. It looks as if PDF/X-3 will be superseded by PDF/X-4 before the standard actually had any major impact on the industry.
Which other PDF/X flavors exist?
Below are other PDF/X flavors that are either actively used in the market or may become popular in the future.
- The first standard, created for black&white, CMYK or spot color jobs.
- This is a standard that originated in the USA but is also popular in Europe.
- An updated version of PDF/X-3 which adds among others support for transparency and spot colors.
- Derived from PDF/X-4, allows external images.
PDF/X is just the starting point
If you think all of the above restrictions make sure that you get perfectly printable PDF files, think again. There are no rules in PDF/X that state that images need to have a certain resolution. A file with 50 dpi images in it can be a valid PDF/X-3 file yet the printed result will be horrible. PDF/X is meant to be a standard which is independent from the specific production requirements of a type of printing.
GWG is an industry organisation which took the PDF/X standards and then added on top of that a set of rules to cover specific types of printing. There is a standard for exchanging files for magazine printing or for newspaper printing. In fact, there are 13 different standards depending on the type of printing, all of them with PDF/X as the starting point.
If you want to get absolutely perfect PDF files for the type of jobs that you print, head over to the GWG site and check out their specifications. In a lot of countries, the national trade organisations recommend printers, trade shops & publishers to use the GWG standards to exchange files.
How to create a PDF/X-3 file
The cheapest solution is probably to purchase and use Adobe Acrobat 6 or later. From version 6 onwards, PDF/X-3 support is build right into Acrobat Distiller, the module that is used to create PDF files.
To convert an existing PDF file to a PDF/X-1a file, you can use a plug-in for Adobe Acrobat Professional. I have used Enfocus PitStop myself and have read and heard a lot of positive comments about the tools from Callas software.