Alt Text for Images in Adobe Acrobat (PDF)
Images need alternate text (or alt text) to convey information. Screen reader programs cannot determine the meaning of images and depend on the alt text to make them accessible to users who are visually impaired. Decorative images can be marked as background or given an empty alt attribute.
See the knowledge base article titled, "Adobe Acrobat Setup for Remediation" if the Accessibility tool is not in the Tools pane.