PDFs for non-dummies

Adobe PDF is a superbly flexible file format that’s become the norm for sharing documents. It’s also increasingly dominant as a way of delivering desktop publishing (DTP) jobs to print shops – but the plethora of output options has many users questioning whether it really makes things easier.

In this article we’ll explain all the basics of PDF for prepress. We’ll focus on output from the leading DTP applications, InDesign and QuarkXPress; graphics programs such as Photoshop, Illustrator and Corel Painter also have PDF export facilities, and similar issues apply.

Where to begin

There are essentially three ways to produce a PDF. The simplest is to use the PDF generator built into Mac OS X, which is accessible from almost every application via the Print dialog box. In a drop-down menu at the bottom left corner is an option to Save as PDF. This does exactly what it says on the tin, but you’ll notice a suspicious lack of options. If you need a quick copy of something in a format that both you and any other user can easily open and will look roughly as intended, it’s very handy. As a way of storing complex documents ready for reliable and accurate reproduction, however, it’s about as effective as taking a picture of the screen with your iPhone.

Apple’s PDF creator was introduced as a simplification of the original route from application to PDF, which was via Adobe’s Acrobat software and specifically the Distiller application. The workflow was to save your DTP document as a PostScript (PS) file – not to be confused with the similar EPS (encapsulated PostScript) format traditionally used in prepress environments to store vector drawings and clipped bitmap images – and then import this file into Distiller, which converted it to a PDF. Alternatively, a shortcut was to install the Adobe PDF printer driver, which accepted PostScript output from your DTP application – much the same as an actual PostScript printer – and generated a PDF from this, cutting out the additional stage of saving the PostScript but at the expense of some flexibility.

These methods are still in widespread use, and the PostScript/Acrobat route has a number of potential advantages, despite being somewhat unwieldy. Outputting PostScript is relatively foolproof; the resulting files are large and pretty much impenetrable – you can’t view the pages you’ve created – but they store all the information required to print the document without requiring the user to make a lot of choices.

At the simplest, the user can drag a PostScript file onto Distiller’s window to set the PDF creation process in motion. For greater automation, Distiller allows Watched Folders to be nominated, so that any PostScript file saved to a certain location is automatically turned into a PDF. When multiple files arrive faster than they can be processed, Distiller queues them.

PDF workflows

In the past, one downside of this two-stage approach was that preflighting happened after the designer ‘pressed the button’, and prepress errors such as invalid spot colours would result in the file bouncing back to the user a few minutes later, wasting time and effort. However, the DTP apps now have built-in preflighting, and if this is correctly set up it should be possible to catch most problems before export. InDesign CS4 even offers live preflighting, so a ‘traffic light’ constantly displayed in the application window’s status bar lets users know if the document has any issues that would arise at output time.

In a publishing house or design agency, PDF conversion is often performed on a server, with PostScript files delivered from designers over a network, whether locally or even via the Internet. Adobe offers various levels of Acrobat solution, and third party server-based PDF creation products such as Agfa’s Apogee are also popular, along with enterprise solutions for non-press PDF sharing workflows in corporate environments. Separating PDF creation from layout avoids keeping creative staff waiting for conversions to complete and allows production to be managed as a discrete task. Output from multiple designers and editors can be queued and processed efficiently; staff who need to art-check or proof-read the resulting PDF can be notified automatically when the file is ready. A controlled and consistent centralised PDF function aids efficiency and quality control.

For the individual user simply wanting to produce press-ready PDFs, this kind of workflow may be overkill. Here the third option comes into play: direct PDF export from DTP applications. Both InDesign and QuarkXPress now have comprehensive built-in PDF features, with a number of preset job definitions and the ability to save and load custom job options. This makes it unnecessary to invest in Acrobat Pro unless you have specialist requirements. An increasing number of other graphics applications can also generate their own press-ready PDFs.

If you need features not offered within your application, such as more detailed preflighting and perhaps automatic online delivery to your printer, third party utilities such as Enfocus Instant PDF integrate with the main design apps to give you more control over your workflow.

Standards and specs

It’s all very well having a full range of PDF options at your disposal, but how do you know which settings to choose? If the answer that springs immediately to mind is ‘I don’t’, you’re not alone.

Although PDFs have been used in prepress workflows for a decade, it’s only quite recently that the printing industry has really got to grips with the issues involved, and there’s still a lack of consensus about how PDFs should be supplied and output. The JDF ‘job definition format’ has been introduced to convey detailed instructions through the whole workflow, ensuring files are correctly created and handled from design to press, and is fully supported both by Adobe InDesign and by the Job Jackets feature in QuarkXPress version 7 and higher, but it’s still not very widely used, especially by smaller publishers and agencies dealing with printers on an ad hoc basis.

Publishers who accept PDFs from advertisers often insist that files are created to an industry standard specification such as PDF/X-1a. The PPA’s Pass4press guidelines provide more flexible and detailed instructions with the same aim of standardising files, but many users find them daunting.

When sending files to a printer, you should be able to establish the appropriate job options for a PDF simply by asking. In practice, you may get little response beyond ‘press quality’, which is about as useful as a doctor asking someone’s blood type and being told ‘red’. So you’ll need to apply some basic knowledge of the pitfalls of PDF delivery in order to avoid them.

On choosing File > Export > Adobe PDF in InDesign or File > Export Layout as PDF in QuarkXPress 8, you’re offered a small range of preset specifications (Quark calls them ‘PDF Styles’). For prepress purposes, ignore the low resolution and ‘high quality printing’ formats (the latter are for output on a desktop printer). That leaves a choice of generic ‘press quality’ or industry standards such as PDF/X-1a. ‘Standards’ sounds good, but there’s a catch: the older the standard, the more likely it is to be accepted by your printer, but the more features of modern documents it’ll prohibit, including transparency.

Transparency and flattening

Transparency doesn’t just refer literally to transparent elements in your designs; it’s the technology that enables all those nice 21st Century effects like blending modes and soft shadows. However, saving a file without transparency doesn’t mean forgoing all the effects. The trick is to ‘flatten’ areas of the page where effects exist, turning them into a raster image – a picture of the page, if you like, rather than a proper scalable vector description. This is done automatically in software as part of the process of generating a PDF to a specification such as PDF/X-1a, the longest-established standard and still the only one that’s really widely supported.

Unfortunately, flattening has its problems. Firstly, any rasterised area has a limited resolution, typically 300dpi (dots per inch) for press-quality PDFs. That’s enough to keep photographic or ‘soft’ imagery looking sharp, but ‘hard’ elements such as black text – what printers call the ‘line work’ – won’t look as crisp as if they were delivered as vectors and rendered at the full press resolution, typically 2400dpi. If a soft shadow, for example, falls across a text box, the shaded part will be flattened while the remainder of the page isn’t, and on close inspection you may be able to see the joins.

To minimise this, avoid transparency effects interacting with text unless they really need to, and ensure all text boxes are brought to front, lying on top of other elements, so that they’re not flattened unnecessarily. This may be easier if you create a layer containing all your text frames. Because black text is normally output as an ‘overprint’ – that is, no white area is cut out of underlying elements to make room for it, the black ink just sits on top – the software can leave the text as vectors, even if underlying graphics are flattened.

In InDesign, you also need to ensure the document’s working transparency blend space is the same as the output colour profile. That may sound like the kind of gibberish that gives prepress a bad name, but all it means is that the software has to use some method of working out how transparent bits look, and if it has to switch methods during PDF output you may find areas of the page don’t match each other. Recent versions give a warning at the final step of PDF export if the working blend space is wrong for the specified output profile, and you can alter it under Edit > Transparency Blend Space.

Since flattening can be so glitchy, it might be better to keep transparency effects intact in the PDF and leave it to the printer’s equipment to rasterise them. More recent versions of PDF, from PDF 1.4 (Acrobat 5) onwards, can handle transparency without flattening, but using them means saying goodbye to the reassurance of PDF/X. Instead, start from the generic ‘press quality’ setting, then go through the list of options and check them against our advice.

And finally…

While dealing with the more esoteric settings, don’t overlook the obvious. Does your printer want all your pages in one file, or one page per PDF? Should double-page spreads be supplied as such or split into singles? These options are on the first screen of each program’s options.

Also here in InDesign, and in the preceding Export as PDF box in QuarkXPress, is a field where you can set exactly which pages you want to include in the export. Use hyphens for ranges (1-5) and commas to separate discontiguous pages (2-3, 5, 14-17). In both applications, you have to include the section prefix for any pages that have one; the prefixes may not all be visible in the Pages palette, so check them before choosing the Export command to avoid frustration.

Finally, always keep in mind that a press-ready PDF is a finished product, not a work in progress. Although it’s theoretically possible to edit a PDF in software such as Acrobat Professional, in reality there are very few changes that it’s practical to make. Check your PDF carefully onscreen before sending it, and if anything isn’t right, go back to your DTP application to correct it before re-exporting the PDF.

PDFing is far from foolproof, but as they say on Crimewatch, don’t have nightmares. Given a basic understanding of the issues, you should soon be firing off files with confidence.

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It’s sensible to downsample images to around 300dpi, as higher resolutions will increase file size and processing time without visible benefit, but avoid excessive compression. Note that Adobe’s ‘High’ JPEG setting means high quality, while Quark’s ‘Low’ means little compression, ie high quality.

In the past, all image files had to be saved and placed in CMYK format to enable correct output. You can now convert all colours to CMYK (leaving spot colours such as Pantones intact if required) on export, so it doesn’t matter how linked images are originally stored. In InDesign, choose the ‘Preserve Numbers’ option to ensure CMYK colours created within the application don’t shift colour on output. Set the Destination profile to your printer’s recommendation or a generic press CMYK specification.

In QuarkXPress, choose the Composite CMYK option for similar results. The conversion method and destination profile can’t be set here; if you need to tweak them, first go to Edit > Colour Setups > Output, click Composite CMYK and then Duplicate, rename the Setup and adjust the options, then go back to File > Export > Layout as PDF and select your new Setup under Options > Colour > Setup.

Choosing a PDF-X specification forces compatibility with the ancient PDF version 1.3, and transparency flattening kicks in. Selecting a higher PDF version will grey out the Transparency Flattener settings, as transparency effects will be kept intact in the PDF. However, the file will no longer meet the PDF-X standard. QuarkXPress always flattens transparency, using the settings under Transparency in PDF Export Options.

Always embed all the fonts used in your document; even if the printer owns the same fonts (and they’ll normally need to in order to comply with licensing), this avoids any possible mismatches. Both QuarkXPress and InDesign embed fonts in PDFs by default.

Check with your printer what registration marks are required, or go with the defaults here. Remember to leave the requested amount of bleed (area beyond the paper’s edge) around the page; printers almost always ask for 3mm all round.

Adobe Distiller, now part of Acrobat 9 Professional, generates PDFs from PostScript output. After the required settings are applied, files can be dragged onto the Distiller window or dropped into watched folders. In QuarkXPress 8, the workflow options under Preferences > PDF let you output PostScript to a specified folder.

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PDF plug-ins

We’ve mentioned that add-ons such as Enfocus Instant PDF can provide enhanced PDF export from within your graphics software. Utilities such as Enfocus PitStop 8 Professional and Markzware FlightCheck Professional are also available to help you check and if necessary correct PDFs on output to streamline your workflow and avoid errors.

To help avoid prepress glitches, printers can use Adobe’s PDF JobReady technology to supply customers with a plug-in that automatically generates PDFs to the correct specifications. It’s not widely used yet, but could help make commercial printing better controlled.

Other add-ons address specific requirements. For example, when exporting a PDF you can format it appropriately for your workflow, but what if you need several different PDFs of each document – perhaps one for press, another for syndication and a third for online? Outputting them all would be a pain. Software Robotics’ PDF-X-Robot automates this kind of task while adding extra preflighting checks to ensure press-ready files match a printer’s specific requirements.

Another standard PDF feature is to choose what level of downsampling and compression are applied to images to limit the size of the file and thus how long it takes to transmit and process. If the built-in options aren’t flexible enough, a utility such as LinkOptimizer can help by using Photoshop scripts to post-process linked images on or before output.

PDF servers

When you have several users needing to generate PDFs on a regular basis, PDF server software is the answer. Adobe’s Distiller Server 8 is used by organizations including the Guardian, providing centralised control over job options for all purposes, including prepress, electronic distribution and archiving. Easy integration with Adobe CS applications is an obvious benefit.

Agfa’s :Apogee solutions are probably the most familiar of the third party alternatives. There are many different ways for users to upload files securely to an :Apogee PDF & Proof server, whether over local or remote networks, and the resulting PDFs can be delivered automatically into printing workflows such as Agfa’s own :SherpaRemote. Other Apogee products cover the entire print workflow.

Enfocus is another major player in PDF creation. The PitStop Server solution supports the company’s Certified PDF technology, which applies rigorous checking and correction to ensure files comply perfectly with prepress industry standards such as ISO’s PDF/X formats and the Ghent PDF Workgroup specs. It also integrates with other Enfocus products including the Switch series of publishing automation tools and the PDF Workflow Suite.

Other server solutions include Helios PDF HandShake UB+, which is scalable from a few users to hundreds and covers a variety of preflighting and automation functions. Unlike some rivals, the server-side software is Mac-compatible and can run on an Xserve.

First published in MacUser, 5 June 2009

Tagged as: Design, InDesign, MacUser, Media, Photoshop, QuarkXPress, Tutorials