PDF

The vast majority of print jobs are co-operative efforts involving several companies. Designers create the artwork; prepress companies often finalise the artwork technically; publishers collate input from several sources into one publication, and printers let their presses hum producing the end product. Transferring the documents in a way that is both simple and technically reliable is a key challenge for the graphic arts industry.

The portable document file format conceived by Adobe in 1992, although perhaps not perfect at that time, is currently the standard document file format for file exchangeability in the graphic arts community.

The strengths of PDF

All-in-o

A PDF file is a container. It can contain all the components needed within the file (fonts, images, illustrations, colours ....)

Cross-platform

PDF is conceived to look identical on any computer platform.

Compact

In general, a PDF file is significantly smaller than its equivalent in another file format (almost 5 times smaller). Elements in the file are compressed with a suitable algorithm depending on the type of element, and images can be re-sampled to an appropriate resolution.

Easy to use and inexpensive

Almost all up-to-date creation and layout applications allow PDF’s to be exported directly from within the native application. This gives the users the possibility of creating a PDF ‘on the fly’, making it easy to use. Because of this, there is no need for an external application to create a PDF.

Structured

The shape and attributes of every component are stored inside the file, including text, fonts, colours, Bézier curves, vectors, and images. Shapes and attributes can be accessed and modified individually, without touching anything else in the file. As a result, last minute changes can be made to the document, using PDF editing tools.

Public file format

Adobe authors, (and controls), the technical PDF specifications. The company publishes these specifications, making them accessible to anyone. As a result, any determined party can build tools around the PDF format, and it also becomes possible to refer to these public specifications in official ISO standards, such as PDF/X.

Unfortunately, the world of PDF is not perfect - PDF suffers from the weaknesses of its strengths. It is such a flexible format that you can use it to transmit a contract to your client for review, post flyers on the Web, and transmit ads to a magazine publisher. The same product is used, the same actions are performed, however different settings should be used in each case.

Today everyone can create a PDF file, regardless of whether you are an experienced pre-press operator, or a novice designer, often unaware of the technicalities of the process. It is therefore essential to check (or “preflight”) a PDF file against the appropriate requirements before sending it to the next contributor in the process.

Other shortcomings of PDF are highly detailed technical ones, or concern limitations of the products used to create or consume PDF. Many of these issues can be detected during a detailed “preflight scan” of the file. But in general, of course, there is no automatic “miracle cure”. In these cases a good editing tool - and a responsive support department - may adapt the work in order to complete the job.

In summary, to keep PDF the perfect file format for the graphic arts industry, we need standardisation.

Over the last few years, Certified PDF® technology has become part of many companies’ PDF standard operating procedure. Everyone realised that a number of important requirements are going unfulfilled by the PDF specifications. These needs all revolve around the same issue: PDF files have no “memory”.

Performing a preflight operation leaves no trace in a traditional PDF. It is impossible to trace edits, to compare the file before and after the editing session, and to identify who has made those edits. This can cause finger pointing and denial of responsibility when a print job ends up looking unrecognisable to the client. To cater to these needs, Certified PDF technology was developed by Enfocus, an Artwork Systems brand. A Certified PDF file is self-aware. It records and tracks whether or not it was preflighted, the settings that were used, and whether or not the file passed the test. A complete log of all edits performed on the file is recorded and available within the file.

Standardising PDF for print

Not all PDF files are suitable for print purposes, as in order to be fit for print a PDF must comply with a set of more restrictive criteria. Several organisations have taken the initiative to define these criteria.

The first organisations to define such specifications were large individual printers and publishers, who defined requirements and guidelines based on their own internal workflows. Later, national industry associations started defining specifications for their respective industry segments. Over the last few years two important international initiatives developed: PDF/X and the Ghent PDF Workgroup. PDF/X defines a common ground for PDF used in print workflows, while the Ghent PDF Workgroup (www.gwg.org) aims at defining industry segment-specific settings.

A number of organisations took the initiative to define a common ground for PDF used in print. A working group was created inside the Committee for Graphic Arts Technology Standards (CGATS), initiated by the American Digital Distribution of Advertising for Publications (DDAP) and the Newspaper Association of America (NAA), and involving several industry vendors and users. The resulting PDF/X specification (ISO 15930) is a true standard, similar to standards for camera film sensitivity (“ISO400”) or quality management (ISO 9000). The objective of PDF/X is to allow “blind exchange” of PDF Files in a graphic arts workflow.

PDF/X is designed to be sufficiently generic to cover all market segments of the print industry: from newspaper ad delivery to oversized poster printing.

The Ghent PDF Workgroup

The objective of the Ghent PDF Workgroup is to take PDF/X a step further, by developing more segmented and detailed specifications (for instance packaging printing, office documents printing, large file format printing...).

It all started when Medibel+, a Belgian association representing the players in the ad delivery process, decided to set specifications for ads exchanged in the Belgian market. Roularta, Belgium’s largest publisher and magazine printer, was in charge of the project. It decided to hold a pragmatic bottom-up approach to the issue: what are the typical problems with PDF files received from designers, and which preflight product best detects those issues. As a result of these tests, Medibel+ expressed its specifications as an Enfocus PDF Profile (a set of preflight rules). These specifications were distributed to the parties delivering ads, so they could preflight files before sending them out to the publishers.

The approach was a success, dramatically reducing error rates of incoming files. Industry associations in nearby countries, active in ad delivery and commercial print, took notice and adopted the settings, guidelines and best practices.

All along, Enfocus worked actively with these associations, assisting with field tests, adding product features to solve residual problems, and helping to minimise the differences among specifications in neighbouring countries.

At first glance it may seem complex. However, implementing PDF specifications is really not that difficult. The Ghent PDF Workgroup and the various industry associations have made every attempt to keep things simple. All necessary information is available from their respective websites, providing ready-to-use tools and guidance.