PDF/X comprises a number of standards published by the International Organisation for Standardisation.
PDF/X: These describe the properties of printing templates as PDF files, in order to allow data to be transferred from pre-print to printer while preserving the original template. PDF/X 1a therefore describes true-colour reproduction using the CMYK colour model, while PDF/X 3 expands the standard to include the RGB colour space. PDF/X standardises a subset of the Portable Document Format (PDF) in order to meet the printer technology industry’s need for corresponding print templates.
The standards forbid PDF elements that could influence a printer output’s predictability, as well as those that cannot be meaningfully printed (such as video and audio). In addition, precise details necessary for printing are mandated, such as trim, colour details and fonts used. The goal of these standards is to avoid or at least minimise a range of problems that can occur when sending files from DTP or graphic-design programs to printing presses.