Create accessible PDF documents in InDesign
Step-by-step instructions for creating accessible PDF files
If you’re publishing PDF documents on the ETH website or sending them via email, they have to meet accessibility guidelines as required by the Swiss Federal external page Law on Equal Opportunities for the Disabled (German). Accessible PDFs benefit all readers because they are clearer and more structured.
1. Templates
Use the current templates in the Corporate Design style guide. They contain paragraph styles with export tags that are important to the structure and semantics – and thus the accessibility – of PDF documents.
Please note: For accessibility reasons, text boxes can no longer be coloured or use margin spacing. If text is placed on a coloured background, the text fields need to be marked as a separate element on a coloured field. Otherwise the output is prone to mistakes.
2. 2. Text formatting
2.1 Use paragraph and character styles consistently
Please make consistent use of paragraph and character styles when formatting text. You can adapt and edit the styles as needed.
2.2 Manual breaks in text
Don’t simply use hyphens to create word breaks. Instead, you should use the “Discretionary hyphen” command, which is Cmd+Shift+- on a Mac and Ctrl+Shift+- on Windows. You can prevent a word from breaking by placing a discretionary hyphen at the beginning of the word using the same keyboard shortcuts.
2.3 Don’t use empty lines
Avoid using empty lines. Line spacing settings are saved in style sheets under “Spacing before” and “Spacing after”. The reason is that empty lines are read by screen readers as “empty, empty, empty”.
2.4 Lists and numbered lists
Use the list function to create bulleted lists and numbered lists. Screen readers do not correctly interpret manually entered characters.
2.5 Hyperlinks and email addresses
Hyperlinks and email addresses can be created in InDesign by going to Window > Interactive > Hyperlinks. Enter the complete web or email address in the dialogue box and select the “Hyperlink medium” style. Copy the address as alternative text into the field under “Accessibility”.
3. Text layout
3.1 Link all frames in a story
Be sure to thread all frames in a story together. Exceptions: Headlines and leads don’t necessarily have to be linked to the text frames that follows.
4. Create a story
4.1 Add all relevant frames to the story
To prepare for exporting the PDF, add all relevant frames to the same story in the Story panel (Window > Story). Create a story for each topic by clicking the framed plus symbol at the bottom of the Story panel. Use the plus symbol to add the text frames in the right sequence. The sequence can be corrected later by shifting the frames around.
Please note:
- If text is already threaded together, it’s enough to incorporate the first text frame.
- Image frames that are anchored in the text don’t need to be added (see “Anchor images in text”).
- Be sure that the “Use tag sequence for PDF with tags” option is selected in the Story panel.
5. Alternative text for images and graphics
5.1 Add alt text under “Object export options”
If an image or graphic contains relevant content, it needs to have alternative text that describes what can be seen in the image or what information is contained in the graphic. You can compose alt text under “Object export options” (via right clicking on the image). If an image or graphic has already been tagged with alt text, you can extract it via the XMP description function.
5.4 Artifacts and images
If an image is purely decorative, it is marked as an “Artifact” in the object export options. This way it is not integrated into the document structure and is ignored by screen readers.
5.5 Anchor images in text
Screen readers usually read out alt text at the end of the relevant article. You will need to anchor the image if you want the screen reader to read out the alt text at a certain point in the text. To anchor an object, select the blue square on the image frame and drag and drop it to the desired position. The linkage between the text and the image is shown with the anchor symbol.
Tip:
You can use the InDesign text editor by pressing Cmd+Y (Mac) or Ctrl+Y (Windows). It’s much easier to see the anchor position in this view as opposed to the layout view.
6. Tables
Only use tables where they are unavoidable. Assistive technologies like screen readers have difficulty interpreting tables.
If you use tables, you should always use the InDesign table function and format the text using paragraph styles. Headers and footers must be defined as such using the table function.
7. Document metadata
In the file information window, the following information is the minimum that must be included in the Document Title field: “Title of Document – ETH Zurich”. Adding the author, description and keywords is also recommended, as PDF files on websites are indexed by search engines.
8. PDF export settings (job options)
It is necessary to use the correct export settings to make sure that all content and settings in your PDF are exported properly. The following settings are available as a job option (Adobe PDF preset) under the name “Online PDF – accessible”.
8.1 Detailed PDF settings
Select File > Export > Print PDF, click on “Save” and fill out the settings. The following options must be activated:
- Export PDFs with tags
- Include bookmarks
- Include hyperlinks
Compression:
Recommended setting for images: 150 pixels per inch (medium image quality). “Crop image data to frame” should be selected. The goal: the PDF should be as “light” as possible.
Marks and bleed
Leave this empty; these settings are only relevant for printing.
Output:
Leave the settings as shown here (no colour conversion).
Expanded:
Select accessibility options “Show document title” as well as the corresponding language setting.
9. PDF/UA standard
Accessible PDF documents should meet the PDF/UA standard. UA stands for “universal accessibility”. The PDF document needs to contain a certain identifier in the header so that screen readers can recognise it as an accessible document.
Unfortunately it is not possible to embed this information directly in PDFs exported in InDesign. An additional step in Acrobat DC is necessary.
9.1 Add PDF/UA identifier
Go to Edit > Preflight in Acrobat DC. Select “PDF standards” and click on the screwdriver tool. You can add the PDF/UA identifier under Document Information and Metadata. Select this option and click on “Correct”. You will now be asked to save the document again.
10. Check accessibility with Acrobat DC
10.1 Accessibility tools
Click on the Tools tab in the upper left-hand corner of Acrobat. Look for the accessibility symbol and drag and drop it into the toolbar on the right.
Open the PDF document that needs to be checked, select the accessibility tool and click on “Check accessibility”. Don’t make any changes to the dialogue box. Click on “Start check”.
A report will then appear in the left column. If you have structured your article properly, as described in this guide, the structure will usually be displayed corrected. The most important error messages involve missing alt text or the missing PDF/UA identifier.
Note: If you use the templates provided and follow the steps in this guide, you’ll be able to produce good quality accessible PDFs. If there are any small irregularities that get flagged in the report, try to correct them as far as possible. However, do not invest a disproportionate amount of effort. InDesign isn’t error-free in this regard, and sometimes false positives are generated (e.g., untagged objects are reported even though everything was done correctly). “Errors” of this kind do not impact the use of a screen reader in any appreciable way.
10.2 Visualise document structure with the reading order tool
Optional: To get a visual impression of the structure of your document, you can open the Reading Order tool. Display the structure types so that you can see the assigned tags. H1 = main headline; H2 and H3 = two sizes of sub-headlines; P = all text elements.
This tool allows you to manually change the tags. This is not necessary because the relevant tags are generated at export (via paragraph styles in the templates).
You will also see the alt text assigned to the images. The same principle applies: If any alt text is missing, add it at the source (ideally in InDesign) and re-export the PDF.
Tip: Don’t use “Page Content Order” mode. The idea behind this mode is good in principle, but it’s unusable because it displays the sequence completely incorrectly.
