How to Highlight in PDF Documents Online

Need to highlight key lines in a PDF quickly? Highlighting makes reviews clearer, feedback easier to follow, and documents simpler to share.

But there’s a challenge. PDFs are everywhere because they preserve formatting and open reliably on almost any device. That consistency is great for sharing, but it can make PDFs feel like they’re read-only when you want to review or mark something up.

Many viewers hide annotation tools, limit permissions, or don’t support highlighting at all. Below, we’ll show you how to highlight text in a PDF using Smallpdf, how to handle scanned or locked files, and what to do when highlighting doesn’t work right away.

This is the simplest option when you want PDF highlighting that works on any device, in any modern browser.

Step 1: Open Smallpdf PDF Annotator

• Go to PDF Annotator.

• Upload your PDF from your device, Google Drive, Dropbox, or OneDrive.

Step 2: Select the Highlighter

• In the toolbar, select “Highlight.”

• Choose your highlight color.

• Adjust opacity if you want lighter highlights for dense pages.

Step 3: Highlight Your Text

• Click and drag across the text you want to mark.

• Repeat for every section you want to keep.

Step 4: Export Your Highlighted PDF

• Click “Finish.”

• Download your updated PDF with highlights saved in place.

Not all PDFs behave the same way. Smallpdf helps in both common scenarios.

Highlight Selectable Text

If you can select text in the PDF, highlighting snaps neatly to the text line. This looks cleaner for contracts, reports, and books.

Highlight Over-Scanned Pages

If your PDF is a scan, the text is really an image. In that case, you can still highlight visually by dragging over the area you want to mark. If you need selectable text too, you’ll want OCR (more on that below).

If you need to highlight a PDF offline, these built-in options work well for quick reviews.

Highlight a PDF on Mac Using Preview

• Open the PDF in Preview.

• Select “View” > “Show Markup Toolbar.”

• Choose the “Highlight” option.

• Drag across the text.

• Save the file with “File” > “Save.”

Highlight a PDF on Windows Using Microsoft Edge

• Open the PDF in Microsoft Edge.

• Look for the highlight or draw controls in the PDF toolbar.

• Select “Highlight” and choose a color.

• Drag over the text to highlight.

• Save with Ctrl + S.

If Edge doesn’t show markup options, try updating Edge or opening the file with a different PDF reader. For consistent results across devices, Smallpdf PDF Annotator is the smoother option.

You’ve got two solid paths on mobile.

Option 1: Use Smallpdf in Your Mobile Browser

• Open PDF Annotator in your phone browser.

• Upload the PDF.

• Select “Highlight” and drag across text.

• Export and download.

Option 2: Use the Smallpdf Mobile App

If you highlight PDFs often on your phone, the Smallpdf mobile app can feel faster for repeat work.

• Upload your file.

• Choose “Annotate.”

• Use highlight and markup options.

• Export the updated PDF.

If you highlighted something in the wrong color, you don’t need to redo the whole page.

In Smallpdf PDF Annotator:

• Open your PDF.

• Click the highlighted area.

• Update the color and opacity from the formatting options.

• Export again to save the change.

Color idea that stays readable: Yellow for key points, blue for references, green for action items, and red for urgent fixes.

Fixing a messy markup is normal, especially during review rounds. In Smallpdf PDF Annotator:

• Open the PDF.

• Select the highlight you want removed.

• Delete it.

• Export to save the clean version.

With PDF Annotator, you can remove highlights and annotations added using other PDF software, or even change the highlight color in a PDF if you‘d prefer to adjust them instead.

If you’re removing highlights, remove them section by section so you don’t accidentally delete something important.

Most PDF viewers print highlights automatically, but it’s worth checking one setting before you waste paper.

• Open the highlighted PDF.

• Go to “File” > “Print” (or press Ctrl + P / Command + P).

• In print options, look for a setting that includes annotations or markup.

• Preview the print output.

• Print or save as a new PDF.

If you’re sending the file digitally, exporting from Smallpdf keeps the highlights embedded so recipients see the same markup.

When highlighting fails, it’s usually one of these situations.

1. The PDF Is a Scan

Scanned PDFs are images, not text. Highlighting still works visually, but text-based highlighting may not behave as expected. Fix:

• Use visual highlighting in PDF Annotator.

• Run OCR first if you need selectable text.

2. The PDF Has Copy or Edit Restrictions

Some PDFs block markup. You may see disabled annotation controls. Fix:

• If you have permission, unlock the file first.

• Then highlight and export.

3. The PDF Opens in a Viewer That Doesn’t Support Markup

Some viewers display PDFs but don’t support annotation well. Fix:

• Upload the PDF to Smallpdf PDF Annotator and highlight in your browser.

If your goal is to highlight, copy text, and search the document, OCR is the upgrade that makes scans behave like real text.

Here’s the workflow:

• Run OCR on the scanned PDF (OCR is a Pro feature, available with a free trial).

• Open the OCR-processed PDF in PDF Annotator.

• Highlight text normally and export.

This is the best path for textbooks, invoices, printed forms, and older documents that were scanned on a printer.

Highlighting is great for pointing out. Sometimes you also need to fix it.

With Smallpdf PDF Annotator, you can also:

• Underline or strike through important lines.

• Draw shapes to call out areas.

• Add arrows

If your workflow includes review cycles, pairing highlights with short notes reduces back-and-forth later.

If you switch devices often, Smallpdf keeps the experience consistent.

• Highlight only the minimum text you need. Over-highlighting makes the review harder.

• Use two to four colors, maximum. Too many colors slow down decisions.

• If the PDF is a scan, run OCR first when accuracy matters.

• Export frequently during longer review sessions so nothing gets lost.

If you want the quickest way to mark up a PDF, Smallpdf PDF Annotator gets you highlighting, colors, and export in one smooth flow. And if the file is scanned or restricted, you still have clear paths to fix it and finish the job.