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Most non-accessible PDF documents can be made accessible to screen reader users by tagging its contents using Adobe Acrobat Pro. ALA staff can reserve time to use Adobe Acrobat Pro in the ITTS training room, if they don't have it installed on their PC.
Before you start
Before you can add tags to an non-accessible PDF, you must make sure that the PDF contains real text and is not just a series of scanned images. To do so:
- Try to highlight text in the PDF with your cursor. If you are able to highlight text with a text cursor, then it is not scanned.
- If you are only able to draw boxes with a crosshair cursor, then the document is likely one big scanned image.
Convert scanned PDFs to text
If the PDF is scanned, you must convert it to text before it can be tagged:
- Go to Document >OCR Text Recognition >Recognize Text Using OCR.
- In the Recognize Text dialog box, make sure that All Pages is selected and that the Searchable Image output option appears under Settings.
- Click OK.
Add tags to PDFs
The Tags Panel allows you to view and edit tags in the PDF’s tag tree structure. Tags are listed in a hierarchical order that indicates the reading sequence of the document, and they appear as coded element types in angle brackets.
Each element appears in the tree structure by type, title, and the element’s content or a description of the content.
To add a tag tree structure to a PDF:
- Go to View> Navigation Panels> Tags to open the Tags panel.
- Drag the panel to the sidebar, or go to View> Navigation Panels> Dock all Panels.
- In the Tags panel, go to Options> Highlight Content.
For untagged documents, go to:
- Advanced> Accessibility> Add Tags to Document
This will automatically tag document elements with generic (mostly <P>) tags.
Next, correct the element type and hierarchy using the Tags panel.
- Check out the complete tag element reference and tag tree structure example.
- Change the element type:
- Right-click on the tag and select Properties.
- In the resulting window, select the Tag tab
- Use the dropdown to select the correct type from the Type field.
- Add title text, as shown in the image below, to provide additional labeling for navigation. (This is especially useful for complex tag tree structures.)
- Delete all elements with empty content boxes. These should not have been tagged.
- To delete an element or content box, right-click on it and select Delete Tag.
- Combine within one element all content boxes that belong together (e.g. heading text that appears in the document on three separate lines).
- To move an element or content box,
- left-click on it and move it to the appropriate location within the tree structure.
- To add new tags (you will likely need to add container elements),
- go to Tags > Options > New tag…
- Use the pull-down menu to select the tag type. Click OK.
- In the Tags panel, left-click on the new tag to drag it to the appropriate place in the tree structure.
- Click the + to expand the tag structure,
- Click and drag any subordinate tags into the tree below the higher level tag.
Note: While all tags must be properly applied according to their semantic roles, there is usually more than one correct way to mark up a document.
Sequence tags for reading order
The Order panel presents a sequential, numbered list of both the document’s pages and the elements within each page. This list reflects the order in which a screen reader will read content. All order changes made in this panel will be reflected in the Tags panel as well.
- Once you’re done adding tags, go to View > Navigation Panels > Order to open the Order panel.
- In the Order panel, double-check that all tagged content is presented in the proper reading order. To rearrange tagged content, left-click and drag the content icon within the panel.
- Repeat until you are satisfied with the reading order.
Add alternative text to images
Images in PDFs, like those on Web pages, must have alternate text to make them accessible to screen readers.
- To add alternative text to images (not including icons or graphic design elements), right-click on the <Figure> tag and select Properties.
- Enter the alternate text in the Alternate Text box, and click Close. Repeat for all images.
- If a given image has not been tagged, go to Tools > Advanced Editing > TouchUp Reading Order Tool.
- Draw a rectangle around the image.
- Click the Figure/Caption button. Click Close.
- To remove tags from icons or graphic design elements that do not require alternate text, go to Tools > Advanced Editing > TouchUp Reading Order Tool.
- Left-click on the numbered box to select it. Then right-click it and select Delete Selected Item Structure. Repeat for all erroneously tagged items in the document.
Properly tag an existing table
Data tables, like those on web pages, must have tagged header cells and header cell scope specification to be optimally accessible.
- Go to Tools > Advanced Editing > TouchUp Reading Order Tool.
- If the table has not yet been tagged: Draw a rectangle around the data and header cells of the table. Click the Table button. Click Close.
- Right-click on the table, and select Table Editor. All table cells will be highlighted gray (data cell type) or red (header cell type).
- If any cells have been improperly typed, right-click on the cell and select Table Cell Properties. Select the correct radio button (Header Cell or Data Cell) under Type. Click OK.
- Right-click on each red header cell and select Table Cell Properties…
- Use the Scope pull-down menu to select the header cell’s related data cell groups (Row, Column, or Both). Repeat for all header cells.
Never use spanned headers, i.e. two or more stacked rows or columns of header cells, in tables because some screen readers have difficulty correctly conveying their content to users.