What is PDF/X?
PDF/X is an umbrella term for several ISO standards that define a subset of the PDF standard. This is similar to the definition of the PDF/A subset for long-term archiving of electronic documents The PDF/X standard responds to the challenge of ensuring that graphic arts files are written in a way that will reproduce on press exactly as the files’ creators intended. As one of the subsets according to Adobe PDF specification, PDF/X is designed for the blind exchange of final print-ready pages, and is one of the most predictable ways to deliver files bound for press.
Why PDF/X?
Using PDF/X-compliant files eliminates the most common errors in file preparation: fonts that aren’t embedded, incorrect color spaces, missing images, and overprinting and trapping issues. These issues don’t arise with PDF/X files because, by definition, these standards require that all fonts be embedded, appropriate PDF bounding boxes be specified, and color be correctly and consistently defined. PDF/X-compliant files also must describe the printing condition for which they are prepared.
Many creative professionals prefer to prepare all the PDF files they will submit for printing in the PDF/X format, even when the print provider does not specifically require it. The PDF/X format is an efficient way to ensure that a file is validated against industry standards for high-end printing and is print ready.
PDF/X format variants
PDF/X has three variants, PDF/X-1a, PDF/X-3, and PDF/X-4; each variant has an arena of use.
When deciding which PDF/X variant to use?
1. When CMYK files are required, you can choose PDF/X-1a; you’re sending digital ads to be reproduced on a press characterized to a printing standard such as SWOP (Specifications for Web Offset Publications) or SNAP (Specifications for Non-heat Advertising Printing); or when you want to maintain absolute control over a file’s content and color appearance.
2. If your workflow requires transferring data in CIELab or RGB color spaces, with conversion to CMYK occurring later, just choose PDF/X-3. Use PDF/X-3 for complete files that you will send to digital presses or other color-managed environments, or for some digital ads, where you expect the printer to optimize color reproduction for the specific printing environment.
3. For printing artwork with live transparency and layers, you can choose PDF/X-4. Expected to be ratified as a standard in 2007, PDF/X-4 supports transparent artwork and effects, as well as layers. Print workflow systems based on the Adobe PDF Print Engine will be able to process PDF/X-4 jobs natively, without flattening artwork or converting the file to PostScript.
About PDF/X file contents
As PDF/X files require certain contents, prohibit others, and leave some open, it will be helpful to know what’s allowed and prohibited in PDF/X files before creating, preflighting, and correcting them; and when customizing any settings.
Here’s what must be included in a PDF/X file:
- Fonts and images embedded.
- Page geometry (the trim box and bleed box) defined.
- Intended printing condition (output intent).
- Trapping key (Yes = True, No = False) defined.
- Title, creator, producer, creation, and modification dates.
Here’s what’s prohibited in PDF/X files:
- Live transparency, except in PDF/X-4 files.
- Layers, except in PDF/X-4 files.
- Encryption (security).
- Form fields.
- Interactive elements including movies, sounds, buttons, and hyperlinks.
- Annotations within the bleed box.
- Preseparated PDFs.
- Transfer functions.
- Actions and JavaScripts.
- Embedded PostScript®.
