{Using\/ \pkg{pdfx.sty} for producing validating \PDF~documents} {Ross Moore and Peter Selinger} {The \pkg{pdfx.sty} package was originally written by River Valley Technologies and used to help produce \PDF\ documents conforming to the \acro{PDF/A-1}b or \acro{PDF/X-1}a standards. This involved inclusion of information elements, color profiles, and allowance for \XMP\ metadata elements as required in the corresponding published standards. We have revised and updated this package so that it can now be used when producing documents to conform with \acro{PDF/A-2} and \acro{PDF/A-3} (in the `b' and `u' variants), \acro{PDF/X-3}, \acro{PDF/X-4}, \acro{PDF/X-5} (in all variants), \acro{PDF/X-VT} and \acro{PDF/E}. With an appropriate driver engine, it is also able to produce ``Tagged \PDF'', and some requirements for the stricter `a' variants of \acro{PDF/A} are also handled.}