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When Ally flags issues in a PDF, here is what each error means and how to resolve it.
Document Is Scanned but Not OCR'd The PDF is an image of a document rather than actual text. Assistive technologies cannot read it, and users cannot search inside it. If you have Acrobat Pro, go to Tools, select Enhance Scan, and make sure Recognize Text is selected. The higher quality the original scan, the more accurate the result. If you do not have Acrobat Pro, use Ally itself. Next to the file, click the small downward arrow next to the editing wheel, select Alternative Formats, and download an OCR'd PDF. For best results, paste the text into a Word document afterward and add proper headings before saving as a new PDF.
Images Without Alternative Text Images in the PDF do not have alt text. If you have the source Word document, add alt text there by right-clicking the image (Shift + F10), selecting Format Picture, opening the Alt Text pane, and entering a description in the Description field. If you do not have the source document, you will need Acrobat Pro. Go to Tools, select Accessibility, and use the Set Alternate Text option to move through each image and add descriptions or mark them as decorative.
No PDF Title The PDF does not have a title set in its document properties. In your PDF viewer, go to File, then Properties, and type a meaningful, descriptive title in the Title field.
Contrast Issues The document has text that is difficult to read due to low contrast. If you have the source Word document, change the font color there and re-save as a PDF. If you do not have the source but you have Acrobat Pro, use Tools, then Enhance Scans to adjust contrast. Without Acrobat Pro, a program like Photoshop may allow you to adjust contrast.
Heading Structure Is Not Logical (with source document) Heading levels in the PDF skip levels or are out of order. If you have the original Word file, fix the headings there. Open the Navigation Pane in Word (View tab) and click through headings to find any skipped levels. Correct them so the hierarchy is logical, for example Heading 1 for the title, Heading 2 for sections, and Heading 3 for subsections, with no levels skipped. Re-save as a PDF when done.
Heading Structure Is Not Logical (without source document) If you do not have the original file, you will need Acrobat Pro to fix the tags directly. Open the Tags pane through View, then Show/Hide, then Navigation, then Tags. Review the heading tags (H1, H2, etc.) and double-click on any that need to be changed to correct them.
No Language Set The PDF does not declare its language. In your PDF viewer, go to File, then Properties, then Advanced, and select the appropriate language from the dropdown.
Document Is Untagged The PDF has no structural tags, meaning screen readers receive it as an undifferentiated block of text with no sense of what is a heading, a paragraph, or a list. If you have the source Word document, fixing the headings there and re-saving as a PDF is the easiest path. Otherwise, open Acrobat Pro, go to Tools, then Accessibility, and select Auto Tag Document. Review the resulting tags to make sure they are in logical order. Use H1 for the title, H2 for section headings, H3 for subsections, and P for body text. Correct any errors by double-clicking on the tag to change it.
Document Is Scanned and OCR'd The PDF has been scanned and converted to text, but it still lacks structure. It is recommended to add tags so users can navigate from section to section. If you have the source document, fix it in Word and re-save as a PDF. Otherwise, use Acrobat Pro's Accessibility tool to auto-tag the document, review the tags, and correct them as needed using the same heading hierarchy described above.