Preview usually refuses to highlight a PDF because the words on the page are images rather than selectable text. This often happens with scanned paperwork, photographed pages and PDFs exported without a proper text layer, even though the document looks normal on screen.
Apple now documents an Embed Text option in Preview that can recognize text in an image-based PDF. The command appears under File > Export when Preview detects that the document does not already contain recognized text.
First, drag across a sentence with the pointer. If Preview draws a rectangular selection around the page instead of selecting individual characters, the page probably needs text recognition. If the words are selectable but the highlight command still fails, the file may have editing restrictions or a damaged text layer.
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How to make the text highlightable
- Save a copy of the original PDF so you can return to it if recognition changes the layout.
- Open the copy in Preview, choose File > Export, select Embed Text when it is available, then save the result with a new name.
- Open the exported PDF, select the words you need and choose a color from the Highlight menu in the Markup toolbar.
If Embed Text does not appear, try selecting text in another PDF to confirm that Preview itself is working. Apple says the option appears only when text has not already been recognized, so its absence can mean the file contains a text layer that Preview cannot interpret correctly. A fresh export from the app that created the document may solve that problem.
Password permissions can also limit changes. Check Tools > Show Inspector for security information, then ask the document owner for an editable copy if changes are restricted. Do not use a workaround to remove permissions from a file you are not authorized to edit.
For ordinary selectable documents, the process remains the same as in our earlier guide to PDF annotations in Preview. When recognition produces poor results on handwriting, faint scans or complex columns, use a dedicated OCR editor and verify every highlighted passage against the visible page.
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