We all know PDFs. Here we are over a decade and a half into the 21st century and chances are you have probably already read one or more this week and are probably carrying a few around in your pocket right now. Not bad for a file format that originated in 1993!
The longevity of the PDF is down to the fact it still serves a useful purpose. The simple way that PDFs can be created and distributed really does live up to its full name of ‘Portable Document Format’.
PDFs retain the appearance of any designed page. Accurately positioned text, fonts, illustrations and images are embedded inside them so can be reproduced on-screen or in print wherever they go, even when offline. And all at a file size easy to download, email or share – even on the most sluggish connections.
In short, your mum and maybe even your granddad can handle a PDF.
Where the PDF came from
Today Adobe lists 112 different products but back in the early 80s it started building its empire on the PostScript (PS). This was a clever way to package complex print instructions into a single file. But this file could never be visualised until it was printed. Extra tools were needed to let people create, view and edit them and the EPS (Encapsulated PostScript) followed soon after.
EPS was good. But it couldn’t handle much beyond the basics. The PDF was introduced as the replacement and was cleverly built in such a way that it could be developed and expanded upon over the years. Adobe Acrobat is their paid-for tool for creating, checking and manipulating PDFs. It now comes in Standard or Pro versions.
Where the PDF ended up
Each time Adobe brought in new features in Acrobat the version of PDF increased to keep up. PDF1.0 started with Acrobat 1.0 but rather confusingly as the version of Acrobat updated in whole number to 2.0, 3.0 etc. the PDF only updated in points so PDF1.1, PDF1.2 and so on. So in 2001 when Acrobat 5 brought in transparency the PDF version that first supported transparency was PDF1.4. Simple huh?!
PDF1.7 was the 8th and final version before Adobe generously made PDF an open standard with ISO 32000-1.
A modern-day PDF is more like a folder which, as well as holding page content, can also contain multiple layers, security, interactive forms, embedded audio, video, 3D graphics, annotations and more.
Adobe’s vision for the PDF was for use in a ‘paperless office’ concept and I’m told to this day the largest user of PDF is actually the US tax office. The fact that we in the publishing industry latched on to the PDF and now send all files to print as ‘print ready PDF’ was not the reason for its conception.
You can’t print a sound effect
Of all the wonderful things that the later PDF versions expanded to include, many are just not applicable to print and publishing. For example:
- Security has its place but not when it stops your print supplier opening your files.
- Layers might be a nice idea but not when they might disappear or you print the wrong ones.
- Audio and video don’t translate well to inked dots!
And here is the reason that PDF/X is so important…
PDF/X is a subset and a required list
The X stands for ‘Exchange’ or more completely ‘Blind Exchange’ which is when a system can interpret what it is supplied ‘blindly’ – without the need for human interaction.
Supplying your ad this afternoon for tomorrow’s newspaper as a PDF/X means that it will print without a doubt.
PDF/X is an agreed list of what a PDF must contain and also what it must not contain in order to print.
For example the commonly used PDF/X-1a states:
- Your PDF MUST contain all fonts.
- All graphics MUST NOT be RGB.
- Your PDF MUST contain a colour profile (info on how colours should appear)
- Your PDF MUST NOT contain transparency.
Plus lots of other rules which are required for successful printing.
Different types of PDF/X
PDF/X started in 2001 and comes in different flavours. The latest version is PDF/X-5 of which, slightly confusingly, there are various types. An early incarnation was PDF/X-1a and that remains suitable more most print jobs but if you really want to know more about the differences check the excellent prepressure.com site for a good list.
Why a PDF/X is your starting point
Using PDF/X correctly avoids 100% of printing errors. Guaranteed.
But the fact that your PDF will print does not automatically mean that it will give you the results you want.
A simple example is image resolution. Printing a low res image is not an error. Recommended resolution will vary with print methods so what may be deemed a low res image in an illustrated book, may be perfectly normal for a newspaper.
There are no rules about image resolution in PDF/X. Think of using PDF/X as a solid base that you can add other requirements on top of.
How to know whether a PDF is a PDF/X
The good news is you don’t need to know everything PDF/X contains. But if you create or deal with files going to print you should know what PDF/X is and know how to check if a file is a valid PDF/X.
Output using a well made PDF Preset in InDesign will make your PDFs into a perfect PDF/X every time.
Preflighting software such as Adobe Acrobat Pro can also be used to check PDFs against the PDF/X standards and by building PDF/X compliance into the PDF Preflight profiles you use you can achieve a smooth workflow that lets you know all the files you send to print will actually print as expected!
Ken Jones is a publishing software expert with over ten years experience as Technical Production Manager, software trainer and developer at DK and Penguin Group UK. Ken’s company ‘Circular Software’ provides software tools and services for a range of illustrated book publishing customers including Hachette, Macmillan, Penguin Random House, Thames & Hudson and Nosy Crow. Contact Ken via twitter @circularken or www.circularsoftware.com