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Annotating a PDF: A Beginner's Guide to Highlighting and Commenting

August 17, 2025

A PDF is more than just a static document; it's a canvas for collaboration and review. Annotating—the process of adding notes, comments, or highlights—is a core part of working with digital documents. Whether you're a student marking up a research paper or a professional giving feedback on a report, knowing how to annotate is essential.

This beginner's guide will walk you through the basics of annotating a PDF using a free online editor.

What is Annotation?

Annotation is the act of adding a layer of information on top of an existing document without changing the original content. Common types of annotations include:

  • Highlighting Text: To draw attention to important passages.
  • Adding Text Comments: For feedback, questions, or reminders.
  • Strikethrough: To mark text for deletion.
  • Drawing Shapes: Such as circles or arrows to point out specific elements.

How to Annotate with a Free Online Tool

While professional software like Adobe Acrobat has extensive annotation features, you can perform the most common tasks for free with an in-browser tool like Docento.app.

Here’s how you can get started:

1. Highlighting and Covering Text (The "White-Out" Trick) While our editor doesn't have a dedicated highlighter yet, you can achieve a similar effect. To "highlight" text, you can draw a semi-transparent colored box over it. To cover up text entirely, use our white-out trick.

2. Adding Text Comments This is the most common form of annotation.

  • Select the Text Tool.
  • Click anywhere in the margin or on the page where you want to add a note.
  • Type your comment or feedback. You can adjust the font size and color to make your notes stand out.

3. Using Stamps for Quick Feedback Sometimes a simple symbol is all you need.

  • Select the Stamp Tool.
  • Choose a checkmark (✓) to approve an item or a cross (✗) to mark something as incorrect.
  • Click on the document to place the stamp.

Why Annotate Digitally?

  • It's Clean: No more messy handwriting. Digital annotations are clear and easy to read.
  • It's Non-Destructive: You're adding a layer on top of the PDF. The original content remains untouched.
  • It's Collaborative: You can easily share your annotated PDF with others, who can then add their own comments.

The next time you need to review a document, open it in Docento.app, and use the text and stamp tools to make your notes quickly and easily.