How to Highlight Text in a PDF

PDF highlights are different from web highlights in one important way: they are part of the document. When you highlight a sentence in a PDF and save, the yellow band is written into the file as an annotation, and anyone who opens the file in any viewer sees it. That makes PDFs the best format for study notes that must last, and the worst format for a quick "look at this" to someone who only wants a link.

In your browser (no app needed)

Chrome, Edge and Firefox open PDFs directly. Edge has the most complete tool set: a highlight button in the toolbar with several colours, plus drawing and text notes, and it saves back to the file with the disk icon. Firefox's viewer added highlighting in 2023: select text and choose the highlight colour from the small toolbar that appears, then use the download button to save a copy that includes your marks. Chrome's built-in viewer lets you select and copy but does not save highlights; open the file in Edge or a desktop app for that.

1. 1

   Open the PDF in the browser

   Drag the file into a tab or click a PDF link.

2. 2

   Select the passage

   Drag across the text. If nothing selects, the PDF is a scan; see the last section.

3. 3

   Choose Highlight

   Edge: toolbar highlighter icon. Firefox: the pop-up toolbar, then the colour.

4. 4

   Save the file

   Use the viewer's save or download button. Saving is what writes the highlight into the PDF; closing the tab without saving loses it.

On Windows and Mac

On a Mac, Preview is already installed: select text, then click the highlighter icon in the toolbar (or press Shift, Command and H). Click the small arrow next to the icon to change colour or switch to underline or strikethrough. Preview saves automatically. On Windows, the free Adobe Acrobat Reader does the same with the Highlight tool under Comment, and saves with Control and S. Both let you add a note to a highlight by right-clicking it, which is where the reason for the highlight belongs.

On iPhone, iPad and Android

On iPhone and iPad, open the PDF in Files or Books, tap the markup pen, and use the highlighter; or press and hold a word, drag the handles, and choose Highlight from the menu. On Android, Google Drive's PDF viewer and Adobe Acrobat Reader both offer highlight from the long-press menu. On tablets with a stylus, the free-draw highlighter follows the pen, which is faster for reading but harder to search later; text highlights (made by selecting words) remain selectable and searchable.

How to highlight in PDF viewers, side by side

A worked example: marking a forty-page report for a literature review

A postgraduate has a forty-page evaluation report as a PDF and needs three things from it: the main findings, the numbers she will cite, and the places where the authors admit a limit. Here is a session in Preview on a Mac, and it would be nearly identical in Edge or Acrobat Reader.

1. Open the file, press Command + F and type limitations. Preview lists every page with the word; jump to each in turn.
2. Select the sentence that states the limit and press Shift + Command + H. The default colour is yellow; leave it for findings and change it with the arrow beside the highlighter for numbers (a second colour) and limits (a third).
3. Right-click the new highlight and choose Add Note. Type the reason in five to ten words, for example sample only 40 schools, contradicts abstract.
4. When the pass is finished, open the highlights and notes sidebar from the View menu to see every highlight and note in page order. This is the raw material for her review.

The same list, exported or copied into a document with the page numbers, becomes evidence of what she read and where each figure came from. The guide to exporting PDF highlights as a dated record takes it from here, and an annotated bibliography built from PDF highlights is the natural end product for a review.

Pitfalls that lose PDF highlights

• Closing a browser tab without saving. Edge and Firefox hold your highlights in the tab until you press Save or Download. Close the tab first and they are gone.
• Highlighting a copy in an email preview. Mail apps and cloud previews often show a read-only view. Download the file, highlight it, and re-upload or re-attach.
• Free-draw highlighter on a text PDF. Pen marks are pictures, not text annotations. They will not appear in a comment summary and cannot be searched. Use select-and-highlight whenever the text is selectable.
• Flattening before sharing. Some export options (Print to PDF, some "reduce file size" settings) flatten annotations into the page image. The highlight is still visible but no longer editable or listable.
• Two people editing the same file. Highlights added to two separate copies do not merge on their own. Acrobat can import comments from another copy; otherwise agree on one master file.

Expert tips

• Put the reason in the note, not the colour. Colours fade from memory; "contradicts table 2" does not.
• Search the highlights, not the pages. In Acrobat Reader the Comment panel lists every highlight with its text; in Preview the highlights and notes sidebar does the same.
• Keep the original untouched and highlight a copy named with the date. The clean copy is what you send to others; the dated copy is your record.

Use colours and notes, not just yellow

PDF viewers give you several colours, and a small system pays off when you return to a hundred-page report. Our colour code system uses three colours with fixed meanings (claims, evidence, terms). Whatever you choose, attach a one-line note to any highlight whose purpose is not obvious; a note reading "contradicts table 2" is worth more than the highlight itself six months later.

When you cannot select text: scanned PDFs

A scanned PDF is a photograph of a page. Nothing is selectable because there is no text layer, only pixels. You have two options. Free-draw highlighting works on any PDF because it just paints over the image, but the result is not searchable. Better: run optical character recognition (OCR) to add a hidden text layer. Adobe Acrobat (paid) does this under Scan and OCR; the Mac Preview app recognises text in scanned PDFs automatically since macOS 13 for selection; many free tools (OCRmyPDF on the command line, or the OCR option in most scanner apps) will produce a searchable PDF. After OCR, select-and-highlight works normally.

Sharing a highlighted PDF

Because highlights are inside the file, sending the file sends the highlights. If you want to point at one passage without sending a marked-up copy, most viewers can copy a link to a page number (Acrobat: right-click a page thumbnail), and for PDFs hosted on the web you can add #page=12 to the address to open on page 12. Text fragments do not work inside PDFs.

PDFs are where most careful reading still happens. When the same text is also online, the four ways to highlight a web page give you a shareable version, and PDF marks are the natural place to run a claim-by-claim source check. The full list of highlighting guides covers phones, links and keyboard selection.