An introduction to PDF

PDF stands for Portable Document Format. As the name implies, it is a data format that can be used to describe documents. Adobe, the developers of PDF, market software to create, edit and visualize PDF files. Because the specifications of the file format are publicly available and meanwhile even became an official ISO-standard, a lot of other companies develop PDF-related software as well. In prepress, PDF is commonly used as a format to exchange data, either complete pages that need to be printed or advertisements that needs to be included in a publication. The file format is also popular for softproofing and reviewing content, because there are applications that allow you to make annotations on the PDF pages.

What can I do with PDF?

PDF can be used for:

• creating electronic documents. PDF is as close as you can get to ‘the paperless office’.
• exchanging data. More and more applications can read PDF files. Advertisements are often exchanged as PDF files. PDF/X is a special version of PDF that is optimised for this type of applications.
• archiving data. There are tools on the market that allow you to index PDF files so you can create and search an electronic library of PDF files. There is even a special version of PDF, called PDF/A, that is optimized for the long term preservation of electronic documents.
• interactive documents. PDF can be used for electronics forms in which the filled-in data can be stored in a data base.

What does a PDF file look like?

PDF files have a .PDF extension. Their icon looks like this:

Both on Macs and PCs, you will not see this specific icon if no application is installed that can handle PDF files. Nowadays a lot of systems come with the necessary Adobe Viewer application pre-installed.Apple’s OS X system has built-in support for PDF.

How do I open PDF files?

I created a separate page that goes into more detail on this subject. The easiest way to view a PDF file is by downloading the free Adobe Viewer application from the Adobe web site. Adobe Viewer is usually also included on the CD’s that come with many computer magazines. In Mac OS X simply double-clicking a PDF opens it in the OS X Viewer application.

How do I create PDF files?

I created a separate page that goes into more detail on this subject .

More and more applications, such as Corel Draw and Adobe InDesign, have an ‘Export to PDF’ option.

For applications that do not have this option, you simply print your document to a PostScript file and then use a separate application like Adobe Acrobat Distiller to convert the print file to a PDF file.

The Adobe Acrobat application can then be used to jazz up the PDF file and add multimedia stuff, hyperlinks, bookmarks or other stuff.

What are the advantages of PDF?

PDF has a unique number of advantages:

• It is a cross platform standard. This means that somebody can create a PDF file on a Unix workstation and you can open it on a Mac or PC and still see the document just like it was intended to be viewed.
• PDF files can be device independent: they can be printed on a cheap ink jet printer as well as on an expensive imagesetter. This does not necessarily mean that the output will be optimized for each device. A lot depends on the way the document is created.
• PDF files are compact. PDF supports a number of sophisticated compression algorithms as well as a clever file structure to keep the file size of PDF files down to an absolute minimum.
• PDF files can contain multimedia elements like movies or sound as well as hypertext elements like bookmarks, links to e-mail addresses or web pages and thumbnail views of pages.
• PDF supports security. The creator of a PDF file can set various security options. It is possible to lock a PDF so it can only be opened with a password. It is also possible to forbid changing the content of a PDF or disable the option to print a PDF file.

The disadvantages of PDF

Of course there are some disadvantages to the use of PDF as well.

• Contrary to its name, the Portable Document Format is not that portable. Roughly every two years Adobe have released a new version of PDF, each time adding new features or expanding the scope of existing ones. The latest versions of Adobe Reader and Acrobat will ignore PDF features that did not exist when the software was released. While this is an elegant work-around, the fact that there are so many different versions of PDF is not very practical or user friendly.
• Some organisations have always objected to the use of PDF because it was a proprietary file format, owned by Adobe. This was true until January 2007 when Adobe released the PDF 1.7 specs for ISO certification. Some PDF flavors like PDF/X-1 and PDF/A were already ISO-certified years ago.
• PDF tries to be everything to everybody, meaning that it may not be as efficient for a specific task than a tool optimized for that task. You can use PDF on the Internet but in most cases an HTML document may be more efficient. You can use PDF to exchange small graphic elements like ads, drawings or pictures but more prepress applications can handle the EPS file format. You can use PDF for archiving data but sometimes extensive layout features like kerning may keep you from finding a particular word in PDF document.
• PDF is geared towards visualizing documents. Using metadata it is possible to preserve the logical structure of a document. Unfortunately there aren’t that many applications that create such tagged PDF files.
• PDF files are not meant to be edited. Small changes can be made to a PDF file but it is fairly difficult to add complete blocks of text or images to an existing PDF file. There are specialized tools on the market for this but even they cannot always get around this limitation.