PDF’s (Portable Document Format) can be viewed in the Adobe Acrobat software and have emerged as one of the most popular formats for posting documents to the Internet. However PDF’s pose many accessibility problems, although Adobe have gone too great lengths in recent years to improve the accessibility of PDF documents to blind and visually impaired users. Despite this there are still some accessibility issues with PDF’s for blind and visually impaired users.
Before the release of Acrobat 5.0, PDF files were just the graphical output of a page, there was not text although. This made PDF documents impossible for blind users using screen reader to access any of the information contained in a PDF document when Acrobat Reader 5.0 in 2001. Adobe used Microsoft Active Accessibility (MSAA} to incorporate several accessibility features into Acrobat 5.0 and later versions of Acrobat Reader, this allowed blind users to read PDF files with there screen readers, allowing visually impaired users to view documents in high contrast mode, zoom and resize text to fit any size view, and enabled basic keyboard navigation.
In addition several plug-ins made it possible for a web developer to create accessible documents from scanned images via an optical character recognition function. However despite this feature the accuracy of the conversion remains dependent upon the clarity and layout of the hardcopy. When Acrobat 6.0 was released it built on the accessibility features that had been incorporated into Acrobat 5.0.
The web developer should note that PDF’s are only accessible under certain conditions all of which must be true they are:
Another difficulty with PDF documents is that it does not allow a visually impaired user to override the colour scheme used on a PDF if they have difficulty reading it. The web developer should also be aware that the security features of PDF’s can be present accessibility difficulties for blind and visually impaired users. If a web developer wish to encrypt a PDF then it is recommended that 128 bit encryption be used as 64 bit encryption is not accessible to screen readers.
Acrobat 5.0 contains an accessibility checker, which was created by SSB Technologies and is based on their InFocus software. However the accessibility checker does not detect all problems and even when it does find problems the reports that it produces are not considered useful. The report does indicate that there is a problem, but it gives the web developer no indication of where is the document that problem is located or give them any guidance about how to fix the problem.
To overcome condition 1 above, Acrobat 5.0 has a facility for converting Acrobat documents that have been created in earlier versions of Acrobat Reader. In order to use this the web developer needs an accessibility plug-in which is included on the installation CD. However given the poor ability of the accessibility checker this can be time consuming and expensive. The web developer must also be aware that the accessibility checker in Acrobat cannot tell the user where an error is within the Acrobat document. Read More information about converting PDF’s created in earlier versions of Acrobat Reader. Alternatively a web developer could just recreate the PDF that was created in an older version of Acrobat Reader in Acrobat Reader 5.0 or later.
Many scanning programs such as OmniPro and Text Bridge are designed especially to convert image-based files containing text to real text files using Optical Character Recognition(OCR), however the quality of the version depends on the quality of the document being scanned. This allows a web developer to scan their images for legible text. The OCR function will then identify any text contained within the image itself. If the document being scanned is a clear image, then the amount of editing will be minimal. If the document being scanned is poor a lot of editing may be required.
Adobe provides a service for converting PDF’s that are inaccessible into a graphical output type that can be read by screen readers e.g. HTML. A web developer can use this service in three ways form submission, email or entering the URL of the PDF document to converted. If form submission is the chosen method then the web developer needs to enter the URL of the PDF document and the resulting document will be converted. This is particularly useful for small documents, although the converter may encounter difficult when trying to convert PDF documents that contain columns. A web developer should also be aware that the output generated through the conversion of PDF to HTML for example, is not always accessible. Developers should examine the conversion generated markup to ensure its validity and test the PDF with a screen reader to ensure that it is accessible.
There are three types of PDF, unstructured (PDF’s without any additional tags) structured, (described briefly below and in more detail in the Adobe document at the bottom of the page). Tagged PDF’s allow a PDF file to contain logical document structure. This makes them more accessible to the blind and visually impaired. At present very few web developers are currently using tagged PDF’s, the main reason for this is considered to be that many web developers are unaware that they even exist. The problem is made worse by the fact that programs such as Microsoft Word, which allow a web developer to convert a document to PDF do not have any support for converting the document to a tagged PDF, although existing unstructured PDF’s can be converted to tagged PDF’s. This is a very good article about how to create tagged PDF’s.
Adobe included structural facilities within Acrobat Reader 5.0, these allow a web developer to present a PDF document in the usual way and it allows them to structure the document so that the document can be accessible to blind users using screen readers It allows the web developer to insert alternative text descriptions for graphics within a PDF however automated tool support for converting files such as Word documents into structured PDF documents is poor.
Adobe offers there Adobe email conversion service that converts PDF files to HTML. This will return the PDF in HTML or text format as an attachment. Alternativly a web developer can use Adobe's form based submission service that converts PDF files to HTML. This will display the submitted PDF as a HTML web page.
There are also a number of organisations who offer a web developer the service of converting a PDF document into HTML.
An email service is also offered by the Trace center, which can convert PDF documents to text and HTML. E-mail containing PDF files as attachments can be sent to the following addresses: or .
Another service that offers a range of web-based file conversions including PDF can be found on the Go website however, This service will not convert protected PDF documents, for copyright reasons. The Click to Convert website also provides a conversion service for PDF files.
PDF forms are very difficult to make accessible to a blind user using a screen reader. However Acrobat Reader 5.0 or later does allow a web developer to created tagged forms as part of a tagged PDF file (discussed above). Tagged forms allow a web developer to create a tooltip that can provide a blind or visually impaired user with information about what is required in a particular data entry field on the form.
Tagged PDF’s are only supported by recent versions of Jaws and Windows-Eyes, so even if the web developer has made the effort to code the tags on the form correctly and inserted a tooltip for each field, it may still be inaccessible because of lack of assistive technology support. Another problem with PDF forms is that the assistive technology will only speak each individual letter as it entered onto the form by the user. There is no way of providing a method for the user to review what has been typed in the whole field.
Therefore if a web developer wishes to publish a form in PDF format, then it is recommended that they also publish the form in an alternative format that is accessible to assistive technology such as screen readers e.g. Microsoft Word, HTML or RTF.
More information about the accessibility features of Acrobat Reader can be found on the Adobe website. More information about the tools that Adobe provides for converting PDF documents can be found on the Adobe acccessibility tools page. There is also a very useful tutorial on how to create accessible PDF’s.