QUESTION: What is pass4press?

ANSWER: Pass4press is a set of guidelines on how to create a PDF file within certain parameters that are acceptable for magazine publishing within the UK. The PPA (Periodical Publishers Association) pass4press initiative, launched in the year 2000 and now in widespread use, recommends that advertising and artwork providers and receivers preflight and validate their files against elements of the pass4press specification.

See also What is PDF?