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4.4 Portable Document Format (PDF)

Publishing date: May 2002

Adobe's Portable Document Format (PDF) is an example of a proprietary format which over time has become an industry standard.

Documents previously held in a variety of different formats can be saved in PostScript form by using one of the appropriate Adobe Acrobat applications. These can then be read by anyone using the free reader software available from Adobe.

Use each checklist to ensure that your web pages comply with these guidelines

4.4.1 Checklist and summary: Core guidance

Checklist

Summary
There is virtually no limit to the types of file that can be converted into Adobe Acrobat files. They have proved popular with authors and users alike. However, information in PDF is generally considered inaccessible to web users whose disabilities make it difficult to interact with computer technologies.

PDF files retain all of their formatting, type styles and illustrative images. The PDF files use compression, so large documents can be saved using significantly less space than the original files.

Nonetheless there can be performance issues with PDFs and those containing graphics should be tested to check their rendering times.

4.4.2 How PDFs work

Documents or any other form of information for a user of the organisationís website should always be produced in HTML as the standard default, but any other formats can be employed to support this.
The Adobe Acrobat software is proprietary but has also become the standard tool for saving complicated and graphically rich documents in a compressed, platform-neutral format.

Producing PDF files is now a simple process. The software to make PDFs can be installed in a matter of minutes and works with most office productivity software. Once installed, it will even offer new menu options within other applications, such as Microsoft Word.

A PDF file is created in a broadly similar way to sending a document to an office PostScript printer. The PC creates a Postscript file, but instead of sending it directly to the printer, the Acrobat application intercepts it and saves it as a PDF document.

This file retains all the formatting, images and colour whilst also compressing the embedded images usually making the PDF smaller than the original file. The Adobe Distiller application allows the user to specify the degree of compression that is applied to images.

It is recommended that a PDF document be saved at no more than 300 dpi. Specifying higher resolutions, for example, 600 dpi produces large file sizes and does not improve on-screen resolution or indeed most printouts.

The Acrobat Reader software is available for the most popular operating systems and is free. The Reader software works as a plug-in to modern browsers or as a stand-alone application.

One example of a government organisation that has used PDF to good effect, is the Office for Standards in Education (OFSTED). Each of the school reports for state schools is available free of charge on the Web. With a planned workflow process and a dedicated IT system reports can be made available with minimum fuss. A piece of information that could possibly have taken weeks to get hold of before can now be accessed in a matter of minutes.

When PDF files are created care should be taken to ensure that the document is always legible. It is not enough for printers to take a paper publication and save it in PDF format. The following should all be noted:

Important:
Important - Viewers with visual difficulties may find it useful to investigate components that improve the accessibility of Acrobat documents at:

4.4.3 Versions of Adobe Acrobat

PDF has been used on the web for many years, and this longevity has established it as an industry standard. Unfortunately, this has also resulted in some usability issues, as there are now a number of different versions of Acrobat creation and reading tools in use.

Adobeís file format specification (PDF1.4) incorporated in Acrobat version 5 is the newest release and is a major improvement on previous versions. It supports Scalable Vector Graphics (SVG), has a word search facility and has accessibility features. See section 4.4.7 Accessibility and PDFs. As with much purchased software, many production houses upgraded as soon as possible.

The real problem on the Web is that many users have not upgraded their reader software and continue to use an older version. Being a free product it is generally downloaded once and then forgotten about. Unless users have only recently gone online, or they have taken the trouble to upgrade their reader, it should be assumed that the majority of the readership would still be using version 3 or version 4.

Documents created with Acrobat version 4 can be compatible with older versions of the Reader if saved correctly. The version 3 reader may not have all the functionality but the document will be legible. The Acrobat 5 Reader is able to read document formats all the way back to PDF version 1.

These problems must either be completely overcome by the department or clear warnings should be added to the downloadable files to inform users that the files are only compatible with the latest version and that they may have to update their reader software to use them.

section 4.4.7 - Accessibility and PDFs

4.4.4 Metadata and PDFs

When creating a PDF document the author should always include as much detail within the metadata section as possible. This is completed in the following way.

Once an author selects to save a file as a PDF the Acrobat software will want to know what the file is to be called and where it should be saved.
When this information has been filled in, the next screen presented to the author is the metadata-input screen, as illustrated. Here information can be inserted in the Subject and Keywords areas.

PDFwriter metadata screen grab

4.4.5 Security with PDFs

When creating a PDF document in Acrobat versions 4 and 5 the author has the ability to give a document security settings by assigning passwords. This can be used to restrict certain features, such as, copying and pasting, editing and printing. In Acrobat version 5, for example, copying and pasting can disallowed but Content Accessibility remains enabled. The Acrobat security feature can also be used to include a requirement to enter a password before an individual document can be opened and read.

4.4.6 Forms and PDFs

Conventionally, the PDF format has been used as a distribution medium for forms; a PDF form would be downloaded, printed out, completed manually and returned by traditional mail. Adobeís PDF1.3 specification incorporated in Acrobat 4.0 included support for on-line forms. Acrobat 5 has enhanced support for on-line forms.

PDF forms can include familiar elements, such as, radio buttons, check boxes, drop down boxes and text boxes can be built to be completed on-screen. On-line forms can then be submitted for sever-side management using, for example, CGI scripts, XML or via open database connectivity (ODBC) connections into databases.

Accessible Adobe PDF forms can be created using a tagged Adobe PDF file or by converting a pre-existing PDF file using Acrobat 5ís Make Accessible plug-in. Acrobat 5.0 also has a digital signature feature and offers a PKI plug-in.

4.4.7 Accessibility and PDFs

Adobe PDFs have become the portable document format standard for government on the World Wide Web. Hitherto PDF documents could not have been considered as accessible. However, Adobe have taken considerable steps to improve the accessibility of both their Acrobat software and the information contained in their PDF files. Their latest specification (PDF1.4) is incorporated in Acrobat 5.0 and features some of the following usability enhancements:

  • support for assistive technology such as screen readers and/or refreshable Braille output devices through the Microsoft Active Accessibility (MSAA) application programming interface for the Windows operating system;
  • the level of contrast between text and background can make a big difference in the legibility of a page and Acrobat allows users to increase contract by creating custom colour schemes that override the colours specified in a document;
  • the ability to zoom in and reflow text on the screen;
  • keyboard shortcuts to enable navigation without the use of a mouse.

It is important to understand that your legacy PDF documents (those not originally created using the PDF1.4 specification) will remain inaccessible. To give them a level of accessibility you have either to:

  • redistill them from their source material into tagged Adobe PDF files using the PDF1.4 specification in Acrobat version 5, or
  • view your documents using the Acrobat Reader 5 with the Make Accessible plug-in.

4.4.7.1 Make Accessible plug-in

The Acrobat 5.0 Make Accessible plug-in automatically analyses the logical structure of a document and creates a new version of that file that will read more logically with assistive technology. The plug-in allows the users of Acrobat 5.0 for Windows to convert untagged legacy PDF files into tagged Adobe PDF files. A tagged Adobe PDF file is designed to ensure:

  • the information is in the correct reading order on the page;
  • it includes paragraph attributes needed to reflow text correctly;
  • the reliable translation of all text into Unicode so that all characters, for example, hyphens and ligatures, can be read correctly by a screen reader.

4.4.7.2 Accessibility checker

The Adobe Accessibility Checker is a tool intended to identify common accessibility problems in Adobe PDF documents. This tool will, for example, check a document for missing Ďaltí tags on images, and for unrecognisable character encodings. When found they are logged and reported so that you can decide whether or not to fix the identified problem.

4.4.7.3 Validation and testing

Tagged Adobe PDF files should be tested using a screen reader. This will demonstrate how your information will actually be presented to a user and how the reading order and navigational links will work.

4.4.8 Example notification and prompt to obtain the Acrobat Reader

Web managers should consider placing this prompt on all pages that link to PDF documents:

This document is available in portable document format for downloading. The Adobe Acrobat Reader can be freely downloaded from: http://www.adobe.co.uk.

Viewers with visual difficulties may find it useful to investigate services provided to improve the accessibility of Acrobat documents: http://access.adobe.com

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