PDF Techniques
for Web Content Accessibility Guidelines 1.0 and 2.0

PDF Checkpoints

WCAG Guideline 1: PRESENTATION
Design content that allows presentation according to the user's needs and preferences

The PDF Techniques Checkpoints that are covered under this WCAG 2.0 Guideline 1 are . . . . . . .

PDF Checkpoint 1 Ensure That the Text of the Document is Accessible

Ensure that the text of your document can be extracted reliably in logical reading order.

PDF Checkpoint 1.1
Render Characters and Words in Reading Order within the Page

Render words, and characters within words, in reading order within the page-content stream. The ReverseChars marked content may be used when rendering right-to-left text that will be typeset left-to-right (PDF 1.4).

 

Correct PDF Technique:

@@

 

Deprecated PDF Techniques: (What you should NOT do)

Some PDF authoring applications save space by rendering all the characters in one font at a time. Hence, the PDF file may render all the bold characters on a page, then all the normal weight characters. Generally, this will cause characters not to be rendered in reading order.

A PDF page may render all characters left-to-right, top-to-bottom. For a multi-column document, this does not render the words in reading order, since the first line of the second column will be rendered before the second line of the first column.

 

PDF Checkpoint 1.2
Separate words explicitly with spacing characters.

Separate words explicitly with spacing characters. Do not rely on the location of the characters or the division of characters into showstring operations to indicate word breaks. Note that this implies that lines of text for western languages usually end with a trailing space character.

 

Consider rendering the two line example:

Now is the winter
of our discontent.

Correct PDF Technique:

• Position to the beginning of line 1
• Show String ("Now is the winter ")
• Position to the beginning of line 2
• Show String ("of ")
• Position to the beginning of "our"
• Show String ("our ")
• Position to the beginning of "discontent"
• Show String ("discontent. ")

This is the PDF content stream for this example:

/P <</MCID 0 >>B
/CS0 cs 0 0 0 scn
1 i /RelativeColorimetric ri
/GS0 gs
BT
/TT0 1 Tf                 // set the font
0.0004 Tc -0.0004 Tw      // set character and word spacing
12 0 0 12 90 708.96 Tm    // set text matrix
(Now is the winter )Tj    // note trailing space
0.0005 Tc 0 Tw            // set character and word spacing
0 -1.15 TD                // move to the next line
(of )Tj                   // note trailing space
[-200 (our )]TJ           // note trailing space
[-200 (discontent. )]TJ   // note trailing space
ET
EMC

Deprecated PDF Technique: (What you should NOT do)

• Position to the beginning of line 1
• Show String ("Now is the winter")
• Position to the beginning of line 2
• Show String ("of")
• Position to the beginning of "our"
• Show String ("our")
• Position to the beginning of "discontent"
• Show String ("discontent.")

This is the PDF content stream for this example:

/P <</MCID 0 >>BDC
/CS0 cs 0 0 0 scn
1 i
/RelativeColorimetric ri
/GS0 gs
BT
/TT0 1 Tf                   // set the font
0.0004 Tc -0.0004 Tw        // set character and word spacing
12 0 0 12 90 708.96 Tm      // set text matrix
(Now is the winter)Tj       // note no trailing space
0.0005 Tc 0 Tw              // set character and word spacing
0 -1.15 TD                  // move to the next line
(of)Tj                      // note no trailing space
[-300 (our)]TJ              // note no trailing space
[-250 (discontent.)]TJ      // note no trailing space
ET
EMC

 

Note: In the deprecated example above, there are no spacing characters at the end of either line, and there are no spacing characters between the words of the second line.

 

 

PDF Checkpoint 1.3
Use soft hyphens and hard hyphens appropriately.

Use a soft hyphen, identified by a character that maps to the Unicode value U+00AD or 173 decimal, when a line-break hyphen is introduced into the middle of a word.

 

Correct PDF Technique:

If the word "father-in-law" is hyphenated after the first syllable ("fa-ther-in-law"), the first hyphen should be a soft hyphen, and the second and third hyphens should be hard hyphens.

This is the PDF content stream for this example:

BT
/TT0 1 Tf                   // set the font
0.0003 Tc -0.0003 Tw        // set character and word spacing
12 0 0 12 90 708.96 Tm      // set text matrix
(fa)Tj                      // "fa"
/T1_0 1 Tf                  // switch to a font containing soft hyphen
(\255)Tj                    // the soft hyphen is at location
\255
                            // of the font
/TT0 1 Tf                   // switch font back
0 Tw 0 -1.15 TD             // position to next line
[(ther-)3(i)-2(n-)3(law )]TJ// the rest of the word
ER

 

 

PDF Checkpoint 1.4
Use the ActualText attribute.

If text characters are not rendered using the show string operation, they must be marked in the logical structure tree with ActualText attributes containing the derived Unicode values.

 

Correct PDF Technique:

Suppose the word "Arthur" is rendered using an illuminated A.
The structure subtree for this word might contain
<Figure> graphics or image for illuminated A
<Span> "rthur"
The <Figure> structural element should have the ActualText attribute, with value "A", so the word "Arthur" could be extracted.

@@Loretta will come up with a better example here: 7-20-2001@@

 

 

PDF Checkpoint 1.5:
Ensure that all characters codes map reliably to Unicode.

Within PDF, show string operations operate on a sequence of character codes with associated fonts. The character code indicates which of the fonts glyphs to render on the page. However, some fonts do not provide information about the Unicode character that corresponds to the glyph. Without this information, the text cannot be constructed.

So every such sequence of character codes must map unambiguously into a sequence of Unicode code points. Mapping is described:
@@ put link here to section 2.4 on page 102 of Tagged pdf doc, and create or get from LOretta html page as well.

 

PDF Example:

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PDF Example:

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Rationale for the importance of Unicode use:
The Unicode character set is a widely accepted international standard for encoding text. It is non-proprietary, and allows for a richness of character codes. Utilized the world over in internet and network protocols, documents of all kinds, assistive technology devices, user agents, and in an abundance of other areas, Unicode fulfills an important need in local, as well as international communication. It is also the basis on which the World Wide Web's present architecture is, and future architecture will be, built. Therefore it is the best existing system to use for ease of system, device and protocol interoperability for text encoding.
@@ KHS.......Is this accurate? We need help here....@@

 

@@ Also add more info and motivation on why we need to map to Unicode. @@
See http://www.w3.org/International/ and http://www.unicode.org/

PDF Checkpoint 2: Provide Text Alternatives for Images and Graphics

Alternative Text is additional or descriptive text that can be used to describe an image, formula, or other item in the document that does not translate naturally into text.

Since Tagged PDF enables many consumers to recover the contents of PDF pages, a Tagged PDF file should use the alternative text (Alt), actual text (ActualText), facilities.

 

PDF Example:

A pie chart may be described giving the values of the various sectors to provide visually impaired users with more detailed information than generally available from a single caption.

 

PDF Example:

PDF Checkpoint 3: Provide Structural Grouping

PDF Checkpoint 3.1
Provide logical structure (PDF Reference Manual Section 8.4.3) for the document.

• Map structure types to the standard structure types described in Adobe Technical Note #5401. (PDF 1.3)
• Suggested reading Section 3 of Tagged pdf doc @@ Put link here @@

 

PDF Example:

@@

 

PDF Example:

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PDF Checkpoint 3.2
Tag artifacts in the page contents with the /Artifact marked content

This is so that users can control how and whether they are included in the contents of the document.

Artifacts are either:

Artifacts of the printing process, like crop-box markings or the document file name.

Artifacts of the pagination of the document, that is elements that would be absent or present in a much different form if a document was always one big page. like running headers and page numbers

Artifacts of the layout process and typographic style, like a horizontal rule above a footnote.

 

PDF Example:

@@

 

PDF Example:

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PDF Checkpoint 4: Design for User Control of Color and Contrast

Acrobat lets the user control foreground and background color of a document. Text in the original document will use the foreground color. Background elements will use the background color. A background element is defined to be any rectangle that is aligned with the edges of the page (not skewed or rotated) and that covers 50% or more of the page.

 

PDF Checkpoint 4.1
Avoid drawing rectangles behind text that are not background elements.

Even if the rectangle color matches the background color, when the user changes the background color, the rectangle will not change and may cause contrast problems with the new foreground color.

 

PDF Example:

A document with a white background may draw a title by placing characters on a pink rectangle. Since the pink rectangle will not be recognized as part of the background, when the user sets the foreground color to white and the background color to black, the white characters will be hard to see on the pink background.

 

PDF Checkpoint 4.2
Text should not be placed on top of images.

Images are not affected by the background and foreground color settings, so when text is placed on top of images and the user changes the foreground color, the text may be difficult to read.

 

PDF Example:

Black text will be visible on a pastel-colored background image, but yellow text may not be, and changing the background color to black will not change the colors in the image.

 

PDF Checkpoint 4.3
Avoid the use of Color as the Only Means to Convey Information

Does the document avoid using color-coding as the only means of conveying information, indicating an action, prompting a response, or distinguishing a visual element?
@@New checkpoint: Use WCAG wording here. KHS and LGR@@

 

PDF Example:

PDF Checkpoint 5: Identify the Natural Language of all Text in the Document

Specification of the language used for text in a PDF document can increase the accessibility of that document for disabled users. For example, with the language correctly identified, text-to-speech engines can properly vocalize the text, either via a screen reader or some more direct invocation of a text-to-speech engine. KHS

PDF Checkpoint 5.1
Identify the documents primary language.

Use the language tagging facilities (Lang) to specify the natural language of all text in the document. (PDF 1.4)

 

Acrobat 5.0 Tip:

To view or edit the language element Properties in Acrobat 5.0:

1. Select an element in the Tags panel
2. Choose > Properties
3. Enter or change the language property
4. Click OK

 

Correct PDF Technique:

The language may be marked with an instream marking of the form:
/Span << /Lang (en-us) >> BDC (Text to be interpreted as US. English.) Tj EMC

 

 

PDF Checkpoint 5.2
Identify when a language change occurs on the page.

In addition to identifying the primary language as above, individual elements containing content in a language other than main document language should be set to indicate a language change has occured on the page. Thus, this signals the screen-reader to switch to an alternate pronunciation scheme, or to identify alternative hyphenation schemes for various languages.

 

Acrobat 5.0 Tip:

To view or edit the language element Properties in Acrobat 5.0:

1. Select an element in the Tags panel
2. Choose > Properties
3. Enter or change the language property
4. Click OK

 

Note: If it is not empty, the value of this key is a language identifier as defined by [IETF RFC 1766], “Tags for the Identification of Languages,” described in sec-tion 2.12 of the XML 1.0 Specification, http://www.w3.org/TR/REC-xml.

 

WCAG Guideline 2: INTERACTION
Design content that allows interaction according to the user's needs and preferences

The PDF Techniques Checkpoints that are covered under this WCAG 2.0 Guideline 2 are . . . . . . .

PDF Checkpoint 6: Document Navigation

PDF Checkpoint 6.1
Use bookmarks to provide navigation aids into a document.

A PDF file may contain a document outline, allowing the user to navigate interactively from one part of the document to another. The outline consists of a tree-structure hierarchy of outline items, sometimes called bookmarks, which permit the user to go to significant locations in the document.

The root of a document's outline hierarchy is an outline dictionary specified by the Outlines entry in the document catalog. Each outline item is defined by an outline item dictionary. The items at each level of the hierarchy are are chained together through the Prev and Next entries.

 

Provide bookmarks for these Outline items:

• Table of Contents
• Beginning of Chapters
• Index

 

PDF Examples:

Here are examples of a typical outline dictionary and a typical outline item dictionary:

This is the PDF content stream for this Outline dictionary:

// Outline dictionary
21 0 obj
  << /Count 6
    /First 21 0 R
    /Last 29 0 R
  >>
endobj
                                   

This is the PDF content stream for this Outline item dictionary:

//Outline item dictionary
22 0 obj
  << /Title (Chapter 1)
    /Parent 21 0 R
    /Next 26 0 R
    /First 23 0 R
    /Last 25 0 R
    /Count 3
    /Dest [3 0 R /XYZ 0 792 0]
  >>
endobj
 

 

Acrobat 5.0 Tip:

Users can access bookmarks in the Bookmarks Panel in the Navigation Pane. The Acrobat Help documentation, starting on page 91, describes how to work with Bookmarks, creating, editing, and deleting them.

 

PDF Checkpoint 6.2
Use links within a document.

When the content of the document might lead the reader to consult another document, or, another location with-in the same document, provide a link.

 

PDF Example:

@@

 

PDF Examples:

Here are examples of a typical outline dictionary and a typical outline item dictionary:

This is the PDF content stream for this Outline dictionary:

// Outline dictionary
21 0 obj
  << /Count 6
    /First 21 0 R
    /Last 29 0 R
  >>
endobj
                                   

This is the PDF content stream for this Outline item dictionary:

//Outline item dictionary
22 0 obj
  << /Title (Chapter 1)
    /Parent 21 0 R
    /Next 26 0 R
    /First 23 0 R
    /Last 25 0 R
    /Count 3
    /Dest [3 0 R /XYZ 0 792 0]
  >>
endobj
 

 

Acrobat 5.0 Tip:

The Acrobat Help document, starting on page 98, describes how to create and work with links. "Advanced Techniques for Creating Accessible Adobe PDF Files" at http://www.adobe.com/products/acrobat/pdfs/CreateAccessibleAdvanced.pdf discusses how to use the Tags panel to add links to the logical structure tree.

 

 

PDF Checkpoint 6.3
If the value of the link does not describe the target clearly and accurately, provide Alt attributes.

@@

 

PDF Example:

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PDF Example:

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PDF Checkpoint 6.4
Provide a clear, descriptive name for all form feilds

In Acrobat, this field of the Form dialog is called the Short Description. "User name" - the PDF Manual refers to feild name as "user name". The Field Dictionary defines a field in an interactive form. It may contain the optional /TU key to define the description used by messages about the field.

 

Acrobat 5.0 Tip:

Provide a user name (/TU key) for all form fields

 

PDF Example:

This is a demonstration of the short description attached to a text form field named fl-4

This is the PDF content stream for this example:

304 0 obj <<
  /T (f1-4)                            // field name
/Kids [ 1038 0 R ]                     // children of this field
/FT /Tx                                // field type is Text
/DA (/HeBo 9 Tf 0 0 0.627 rg           // default appearance
/AA << >>                              // no additional actions for this field
/TU (your first name and initial)      // short description of field
>> endobj                                    

 

WCAG Guideline 3: COMPREHENSION
Make it as easy as possible to use and understand

The PDF Techniques Checkpoints that are covered under this WCAG 2.0 Guideline 3 are . . . . . . .

PDF Checkpoint 7: Provide Expansions for Acronyms and Abbreviations

Defining key terms and specialized language will help people who are not familiar with the topic you are presenting. Providing the expansion of abbreviations and acronyms not only helps people who are not familiar with the abbreviation or acronym but can clarify which meaning of an abbreviation or acronym is appropriate to use.

 

PDF Example:

The acronym "ADA" stands for both the American with Disabilities Act as well as the American Dental Association.

 

PDF Example:

@@

 

WCAG Guideline 4: TECHNOLOGY CONSIDERATIONS
Design for compatibility and interoperability

The PDF Techniques Checkpoints that are covered under this WCAG 2.0 Guideline 4 are . . . . . . .

PDF Checkpoint 8: Set document protections to permit access

Set the data access restrictions on the document to permit the contents to be accessed by assistive technologies.

• When using 40 bit encryption:

Permit the text and graphics in the document to be copied.
• When using 128 bit encryption:

Set accessibility permission for the document. 128 encryption was introduced with pdf 1.4, and cannot be read with versions of Acrobat previous to 5.0

 

PDF Example:

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PDF Example:

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Assessing the Accessibility of PDF

@@Auto checks: fill in with list of tools that automatically provide results to these checkpoints. Also, in manual provide list of tools that will give warning for possible problem.

WCAG 1.0 checkpoints that are not easily identifiable in WCAG 2.0 checkpoints:

• units of measure
• color contrast