Highlighting text in a PDF is one of the most common things people do when reviewing documents, studying, or giving feedback. But not every PDF tool makes it easy — and some require expensive software just to add a colored mark.
Here's everything you need to know about highlighting text in a PDF, and how to do it for free.
Why Highlight Text in a PDF?
- Study and research — mark key passages for quick reference
- Document review — visually flag sections for colleagues
- Proofreading — draw attention to errors or unclear language
- Reading notes — build a personal annotation layer over a document
Using Annotation Tools in Your Browser
Modern browsers and free PDF tools support annotations. Docento.app includes an annotation layer that lets you add colored boxes and text overlays on any part of a PDF — without uploading your file anywhere.
To highlight a section of text:
- Open Docento.app and upload your PDF
- Use the Text tool to add a text box over the area you want to call out
- For a true highlight effect, use colored boxes or stamps over the text region
- Adjust opacity so the underlying text remains readable
- Export your annotated PDF when done
For a full overview of annotation features, see our annotating a PDF guide.
Highlight Colors and What They Mean
Many reviewers use a color system to organize highlights:
- Yellow — general interest or key points
- Blue — definitions or important terminology
- Green — positive, agree, or action items
- Pink/Red — errors, concerns, or items needing follow-up
Adopting a consistent system makes it much faster to scan annotated documents later.
Tips for Effective Highlighting
- Don't over-highlight — if everything is highlighted, nothing stands out
- Add text notes alongside highlights to capture your thinking in the moment
- Review and clean up before sharing — remove personal annotations unless collaboration is the goal
Sharing Annotated PDFs
Once you've added your highlights and annotations, export the PDF from Docento.app and share it as normal. The annotations are baked into the file, so recipients see them without needing any special software.
For more ways to work with PDFs, check out the beginners guide to editing PDFs.