For over a decade, PDF files have been a convenient way to deliver print documents online, but they remain a challenge to make accessible.
Potential drawbacks include:
- Developers require the full version of Adobe Acrobat to inspect and insert image alt text and other accessibility accommodations into a PDF file.
- The process of repairing PDF files is currently both time consuming and buggy. More training and plugins are required to make PDF forms accessible than to make HTML forms accessible.
- PDF documents are usually formatted to be printed vertically, but computer monitors are generally horizontal. This mismatch causes users to scroll more often than on a Web site, which can be difficult for users with mobility impairments.
- Very large files can be slower to download than an HTML page.
- PDFs consiting of scanned pages are really a series of images, and therefore inaccessible to screen readers. Only an OCR (optical character reader) scanner can save a scanned document as a text file.
- The interface between a browser and a PDF file is not consistent across platforms and browsers.
- The transition between a PDF document and an external Web site is not as seamless as between two HTML documents.
However, there are instances when a PDF can deliver material efficiently.
- To post material that uses technical fonts and/or specialized characters, such as in fields like music, foreign languages and mathematics.
NOTE: Alternative technologies, such as Unicode and MathML, should also be considered for specialized purposes.
- To provide print manuals and print forms online. These would include blank forms, how-to instructions designed for print, contracts, long articles or long user manuals.
NOTE: Alternative file formats, such as Word files or Web pages, should also be considered in addition to PDF.
In order to make PDF files more accessible, consider these recommendations:
- If a PDF is used to create a graphically intense poster or flyer, ensure that the information is also available outside the poster or flyer.
- If a PDF is used to post a report, consider posting the report in a format such as Microsoft word.
NOTE: A PDF alternative can be posted alongside if needed.
- If a PDF is used to post a presentation, consider posting the report in a format such as PowerPoint.
- If a PDF is mandated, generate a "tagged" PDF from a document source whenever possible. The specific method of doing so will vary on the original file format and the operating system. See some options below.
NOTE: Any tagged file should be inspected in Adobe Acrobat to verify that the tagging structure is sound.
- If a PDF is mandated and you cannot generate an accessible PDF, use the repair tools in Adobe Acrobat to ensure accessibility. See the External Links section for links to in-depth tutorials.
- Alert users when a link goes to a PDF file (e.g. "User’s Manual
(PDF)"). Doing so gives notice to all users that a link will be opening
a PDF file, not going to another Web page.
- If you are scanning in material that is mostly text, scan the material in with an OCR (optical character recognition) scanner. This type of scanner converts a scanned image of text to an actual text file. If files are scanned with a regular scanner, the PDF file will consist of a series of inaccessible images.
NOTE: Scanning text with an OCR scanner will also make the transition to HTML easier.
- Avoid converting text with multiple columns into a PDF file. A screen reader may unexpectedly read text across columns. It will also result in additional scrolling as each column is read, making it harder to process for people with motion impairments and some cognitive disabilites.
- Be aware that some security measures on PDF files may disable screen reader access. Be prepared to provide alternative access to visually impaired users.