ANSWER: PDF/X is a term used to refer to a group of technical standards each of which describes a file format that is a subset of the file format described in Adobe Systems Inc.'s PDF Reference. To put it another way: a PDF/X file is a special type of PDF file.

The PDF/X standards have been developed to facilitate reliable exchange of PDF documents among graphic-arts professionals.

The Committee for Graphic Arts Technologies Standards (CGATS) is the organization responsible for developing the PDF/X standards. ANSI (the American National Standards Institute) has delegated to CGATS the task of creating standards for the graphic arts in the USA.

The various PDF/X standards deal with color management and resource management differently. 

Why do we need PDF/X?

In the graphic-arts community, it often happens that a PDF file is created by one person and is then given to somebody else; and the person to whom it is given is supposed to use the PDF file for high-quality printing. In this scenario, sometimes the printed result isn't what was intended. For example,

  • the wrong fonts might be used on the printed piece

  • the colors might not look the way they are supposed to look on the printed piece.

PDF/X is a way of specifying what needs to happen when somebody creates a PDF file so that it's likely to print correctly when they send it to somebody else. The point of PDF/X is that it gives you a label to use when asking for a PDF file if you need to have a high level of confidence that the document will look exactly the way it's supposed to look when printed. In other words, you might say to the person who is creating the file, "Please create the file in PDF/X-1a format."

Doesn't TIFF/IT handle this problem?

For a number of years, the graphic-arts industry has depended heavily on the TIFF/IT file format to ensure reliable reproduction of graphics. For most graphic-arts professionals today, "TIFF/IT" is the label to use when asking for a file format that they know they can rely on for accurate printed reproduction.

The CGATS folks believe the PDF/X standards are going to do for graphic arts what the TIFF/IT standard has already done - but the PDF/X standards have an important advantage over TIFF/IT in that TIFF/IT is completely raster based (so TIFF/IT files tend to be quite large) whereas PDF/X files can be both vector based and raster based (which means that - in many cases - PDF/X files are smaller than TIFF/IT files). It is expected PDF/X will gradually replace TIFF/IT.

What's in the PDF/X standards?

Each of the PDF/X standards specifies the characteristics a PDF file must have in order to meet the criteria set forth in that standard. For example, the PDF/X-1:1999 standard says all colors must be specified in terms of CMYK, grayscale or spot color. Thus, a PDF file that specifies colors in terms of RGB is not a PDF/X-1:1999 file. The PDF/X-1:1999 standard also says all fonts used in the PDF file must be embedded in it. Therefore, a PDF file that uses fonts it does not contain is not a PDF/X-1:1999 file.

Creating PDF/X files

Some software applications that create PDF files allow you to create PDF/X files.

It is important to understand that software geared toward creating PDF/X-compliant files generally cannot guarantee that each file that's created will actually conform to a particular PDF/X-compliance standard. Such software will attempt to generate a compliant file, but the characteristics of the source file (the file that's being converted to a PDF/X format) determine whether or not the file that gets created will be truly compliant.

For example, if you want to make a PDF/X-1a file, all colors in the source file must be defined in terms of CMYK, grayscale, or spot colors. Naturally, this must be taken into account during the page-creation process — upstream from the process of generating the PDF/X-1a file.

Because software for creating PDF/X files can't guarantee compliance, you will need software that verifies compliance. Two applications that can do this are PitStop Professional and PitStop Server.

See also What is PDF?