One of the biggest barriers to PDF accessibility occurs with “image-only” documents. An image-only PDF contains no actual text, just an image of text. This type of PDF is created by scanning a printed page. Lacking any real text, an image-only PDF does not support useful features such as searching, highlighting, text copy, and text reflow; nor will it allow the use of Adobe’s magnification and reading tools.

Software such as Adobe Acrobat Professional can take an image-only PDF and convert it to "Searchable" using a process called Text Recognition, or Optical Character Recognition (OCR). The resulting document has text that you can interact with using a variety of technologies.

Benefits of a searchable PDF include the ability to:

  • Search text
  • Select text
  • Highlight text
  • Create a Table of Contents
  • Listen to text

Click on Enhance Scans in the toolbar.

Enhance Scans menu in toolbar

In the Enhance Scans toolbar that opens at the top of the page, select Recognize Text, then In This File.

Recognize Text menu in the Enhance Scans toolbar

Choose from the All Pages drop-down menu to do either All Pages or a range of pages (it is better not to do longer documents all at once), then click the Recognize Text button. Once the tool finishes running, you should be able to highlight text in the document. Save the document before closing.

Recognize text dialog highlighting All Pages dropdown menu and Recognize Text button

Click on Tools at the top right of the document. When the toolbar opens on the right side of the screen, click on Recognize Text to expand the menu.

Recognize text menu

Select In this File to bring up the OCR dialog box.
Choose a radio button to do either All Pages or just the Current Page, then Click OK. (All pages could take a while on longer documents.)
Recognize text dialog box

Once this finishes running, you should be able to highlight text in the document. Save the document before closing.
Sample PDF with text highlighted