Introduction to accessible PDF

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This chapter explains the PDF standards, what makes a PDF document accessible and different ways to create a PDF. • Accessibility website of the Publications Office of the European Union: https://op.europa.eu/en/web/accessibi... • TRANSCRIPT (shorten) • 25 years ago many different document editors existed, each using its own file format. It is obvious that there was a need for a new file format, which preserved the layout over different operating systems and authoring platforms. The Portable Document Format was developed by Adobe in the 1990s. Each PDF file encapsulates a complete description of a fixed-layout flat document, including the text, fonts, vector graphics, raster images and other information needed to display it. • PDF combines three technologies: a subset of the PostScript page description programming language, for generating the layout and graphics; a font-embedding system, to allow fonts to travel with the documents; a data format, which supports compression, to bundle all page elements and any associated content into a single file. • The free Adobe PDF Reader program allowed an author to send any document to any person using a desktop computer. The recipient just needed to download a recent copy of the reader software and was immediately able to see and read the document presented in the layout intended by the author. • Today PDF has become the de facto standard for the exchange of documents lay outed for printing. It is used on an everyday working basis all around the world, for professional and home use. • PDF is not one standard using a single file format, but consists of a family of different file formats optimised for different applications. This table shows the different PDF standards. • What makes a PDF document accessible? Let's look at a few example documents to gain a better understanding. • Accessibility requires text, not an image of a text. Whether this image is raster based or vector based is of no importance to a screen reader. A screen reader can only detect text with real characters. Text elements require a reading sequence. This becomes even more important if the text content is not presented sequentially, but is broken into several parts, repeatedly interrupted by banners, graphics or any other complementary information blocks. • All non-text information, like images and graphics, require an alternative text describing the element, so that a non-visual user can get an idea of its content. All this additional information can be added to a PDF using tagging. • Let's talk about what tagging is and what it looks like.We see a document that includes chapter headings, graphics, lists and a table. We will create two PDF files following two different procedures. The first approach is to create the PDF using the printer driver. A printer driver has no idea of the meaning of a page element. It does not know if a text is a heading or if it is part of a list or a table. It just knows that the letters using a defined font and size should be placed at a specific position on the page. • The second PDF will be saved using File, Export as, Export as PDF. A dialogue box opens and invites us to select several parameters. We will select the Tagged PDF, which adds the structure of the document, and the Export bookmarks. • At first glance, we notice that the second PDF has bookmarks. Additionally, the second PDF offers tagging information. If we look closer at the tagging information, we can see tags for headings, images, lists and tables. We can see that tags can be nested, so a table has table rows, and table rows have table data cells. All this tagging information is evaluated by a screen reader to present an improved reading experience to a user with a visual disability. • Four different ways to create a PDF. If the document editor offers the possibility of exporting a tagged PDF, then this is always the preferred PDF creation procedure. Only the document editor contains the structure of the document. While editing the document, the user defines headings, lists, tables and other structural information. This information can be embedded in the form of tags in the resulting PDF document to support screen readers. • Some document editors do not offer this functionality. In this case, a PDF can only be created via a printer driver. The resulting PDF will have no tagging information to support users with screen readers. • Sometimes we do not have the document in any digital form. In this case, we need to scan it. Optical character recognition (OCR) is a technology that converts different types of documents, such as scanned paper documents or images captured by a digital camera into editable and searchable text data. Once the text recognition has been finished, the document can be saved as an untagged PDF. • If we have an untagged PDF, we can improve its accessibility by converting it manually into a tagged PDF using Adobe Acrobat Pro. This should always be the last option to choose when creating an accessible PDF.

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