# How to Annotate a PDF: Add Comments, Highlights, and More

URL: https://pdf.net/blog/how-to-annotate-pdf
Published: 2025-04-16
Author: Alex Chen
Reading time: 6 min
Categories: Edit PDF

> Learn how to annotate a PDF online with comments, highlights, and more using pdf.net.

Learning how to annotate a PDF is easy; all you need is the right annotation tool, like pdf.net, to **add comments, highlights, and other markups to your document**. Once you learn how to do this, you can easily collaborate on documents, provide feedback, or simply add notes to files without changing their original content.

Whether you’re a student or a professional, knowing how to annotate a PDF will help you save time and enhance productivity. So, in today’s article, we’ll discuss the different types of annotations you can make and outline the best way to annotate PDF files.

Let’s start!

## Key Takeaways

- PDF annotations are comments, highlights, drawings, and markups that are added to the document to emphasize or explain something without changing the original text.
- pdf.net allows you to **annotate PDF files in three steps**: open the annotation tool and upload your document, add comments/highlights/drawings using the sidebar tools, and review before downloading in your preferred format.
- The** four main types of PDF annotations** include text-based (comments, highlights, sticky notes), markup-based (shapes, drawings, arrows), stamps and signatures for approvals, and interactive elements like clickable links and multimedia.
- **Common annotation issues** like incorrect placement, annotations not saving, and overlapping comments can be resolved by using the eraser tool, ensuring proper file saving, and assigning different colors to each collaborator.

## What Does It Mean to Annotate a PDF File?

Annotating a PDF file means **adding comments, highlights, shapes, drawings, and markups** to provide feedback, emphasize, or clarify content without changing it directly.

PDF annotations are frequently used for their numerous benefits, such as:

- **Improved collaboration**, as there’s no need for emails or long chat threads; everything is visible right there, in the document.
- **Preserved original content**, since annotations don’t change anything; instead, they are overlaid on top.
- [**Enhanced note-taking**](https://learningcenter.unc.edu/tips-and-tools/taking-notes-while-reading/), as this feature allows users to write their thoughts and summaries directly on the document, so they can be easily referred to later.

Essentially, PDF annotations are versatile enough to be used both in education and for various work projects. That’s why it’s important to know how to make them and what types there are.

## 4 Different Types of Annotations

Now that you know what PDF annotations are, it’s time to learn about the **different types you can make**, from text-based to markup-based.

Let’s discuss each type below:

### #1. Text-based annotations

Text-based annotations, like **comments, highlights, and sticky notes**, are the most common annotations you’ll find on documents. If you want to add notes to a PDF for your reference, you can place sticky notes beside the section you want to comment on.

Adding PDF comments, on the other hand, are great for asking for or leaving feedback and [encouraging collaboration in teams](https://www.indeed.com/career-advice/career-development/how-to-increase-collaboration-between-teams). Meanwhile, PDF highlighting can be used to emphasize important sections in the text without changing its original content.

### #2. Markup-based annotations

PDF markup-based annotations like shapes, drawings, lines, and arrows can be used to **highlight the visual elements in the document**. For instance, you can point out an important detail in a graph by adding shapes to the PDF to grab the reader’s attention, then leave a brief comment explaining the annotation.

### #3. Stamps and signatures

Another way to annotate PDFs is by using stamps and signatures to **show that you reviewed or authorized the document’s content**. Some PDF markup software allows you to create digital stamps that say “Approved” or “Reviewed” that you can use to annotate the document, which can be especially useful with files that need multi-level approvals.

While you can also [sign PDFs](https://pdf.net/sign-pdf) digitally, editing or even annotating the PDF afterward can invalidate its [eSignature](https://pdf.net/blog/is-electronic-signature-legal). So, if the text in the document isn’t final yet, you can use a signature annotation to show that you approve of its current version.

### #4. Other interactive annotations

In addition to the usual annotations, you can also add **[interactive annotations](https://pdf.net/blog/how-to-make-pdfs-interactive) like links, embedded multimedia, and form fields **to a PDF file.

For instance, if you are working on a group research project and want to reference external papers, you can highlight the relevant information and annotate the PDF document with a clickable link so other members can view the source of the data.

## How to Annotate a PDF File Online With pdf.net

![Open Your Annotation Tool](https://cdn.sanity.io/images/i16te7yp/production/f05d5392b4ac288962d7bbf048c846b63c27d1a3-1587x715.png?fit=max&auto=format)

To annotate a [PDF file](https://pdf.net/blog/what-does-pdf-format-mean) with pdf.net, you have to **upload your document to our [annotation tool](https://pdf.net/annotate-pdf) **and then** select the type of PDF markup you want **to make. To do this, simply click **Choose file** and select the file you want.

After adding all your annotations, you can **review your PDF **to ensure that there are no stray markings or highlights that can confuse the reader. When everything looks good, click on the **Download** button in the upper-right corner.

Before downloading your file, you can even **change its file name and format**; our tool supports [PDF-to-JPG](https://pdf.net/pdf-to-jpg), -PNG, -DOCX, and -Excel conversions.

Now, let’s take a look at a step-by-step guide to annotate a PDF using different methods:

### #1. Highlighting Text in PDFs

After your document loads, you can start to annotate the PDF using the different **tools on the left sidebar**. One of the best options for drawing attention to a particular part of the text is using the **Highlighter** tool, which looks like a yellow marker between **Marker** and **Eraser**.

![Highlighting Text in PDFs to Annotate a PDF](https://cdn.sanity.io/images/i16te7yp/production/c6a5f9fac34826ae9124c21b517c2bf96dd857bb-1726x859.png?fit=max&auto=format)

To [highlight text in the PDF](https://pdf.net/blog/how-to-highlight-text-in-pdf), select this tool and change its color by selecting one of the color options provided or by clicking on the color wheel to choose a custom shade. Then, simply drag the highlighter across the text you want to highlight until you’re satisfied.

![Annotate larger sections of text all at once](https://cdn.sanity.io/images/i16te7yp/production/09a3496cad132a63b61f4224a156d8f7d6d7f9c2-1062x448.png?fit=max&auto=format)

If you want to annotate larger sections of text all at once, you can adjust the size of the highlighter by clicking and dragging the slider bar below the **Eraser tool**. Once you settle on the right marker thickness, you can annotate the PDF by **drawing directly on the document**.

![Size of the marker](https://cdn.sanity.io/images/i16te7yp/production/953770bf64c97e6124a06bafde3d0c5127766743-1059x305.png?fit=max&auto=format)

If you make a mistake during this step, don’t worry, as you can easily remove annotations from the PDF by selecting the **Eraser tool** and tapping on the section you want to edit.

![Eraser tool on pdf.net](https://cdn.sanity.io/images/i16te7yp/production/a4ff5636eecb23836078d0690f88e772c15de0e2-181x283.png?fit=max&auto=format)

Alternatively, you can select the part of the text using the **Select** tool from the top bar. Then, a menu with several options will appear above the selected text. Choose the **Text Highlight **option, which is the very first on the bar.

![Text Highlight option](https://cdn.sanity.io/images/i16te7yp/production/0638012a732197eb2318de44d18e8980da8b89b1-238x71.png?fit=max&auto=format)

The result is ultimately the same whichever method you use, though selecting the text and highlighting directly may look neater and more precise. That’s because the highlighter marker is a drawing tool, so it relies on your ability to create straight lines.

### #2. Drawing on a PDF

[Drawing on a PDF](https://pdf.net/blog/how-do-i-draw-on-pdf) is as simple as highlighting in our annotation tool, but instead of using the highlighter, you should select the blue **Marker** above it.

![Drawing on a PDF](https://cdn.sanity.io/images/i16te7yp/production/65d5d9dd294e20c1995ba4844415b3f9a134f982-1726x859.png?fit=max&auto=format)

Then, adjust the marker’s color and thickness using the color options and the slider below. Once you’re satisfied, drag the cursor over the text to draw and annotate freely.

![Adjust the marker’s color and thickness using the color options](https://cdn.sanity.io/images/i16te7yp/production/517e78e15d6eef2cdb2ce7fed05a77ca926bae37-620x458.png?fit=max&auto=format)

Once again, you can use the **Eraser** tool to remove any excess drawings or simply click **Undo** to delete entire sections quickly.

### #3. Adding Stamps to PDF

Though there is no dedicated stamp tool in pdf.net editor, you can easily add your stamp by using the **Sign **tool. You’ll find it in the top-right corner of the editor, right next to the **Draw** tool you used for highlights and PDF markups.

![Adding Stamps to PDF](https://cdn.sanity.io/images/i16te7yp/production/c71f6f4097bc11067e828287d637250dc0f20647-326x88.png?fit=max&auto=format)

When you click it, a new menu will pop up, allowing you to either create a stamp by typing the text and selecting a font, drawing it, or uploading an image of it. Choose the option that suits you best, select the color, and click on **Place in PDF**.

![Create a stamp by typing the text and selecting a font, drawing it, or uploading an image of it](https://cdn.sanity.io/images/i16te7yp/production/c512a47f377a5c9b220622956f0126c7dc29bda6-809x486.png?fit=max&auto=format)

Then, you can place the stamp inside the document, choose its opacity, and resize it as needed.

![Choose the opacity of the stamp](https://cdn.sanity.io/images/i16te7yp/production/dd94ca726ece59a3c43bb06ec5647129b8d300d6-581x239.png?fit=max&auto=format)

## How to Edit and Modify Annotated PDFs

To edit and modify annotated PDFs, you can **use pdf.net’s full suite of editing tools**. With our complete PDF editor, you can delete or modify existing annotations on PDFs in a few simple clicks.

To delete existing annotations, select the **Eraser tool** and right-click on the annotation you want to remove. If you need to move an annotation, however, all you need to do is click and drag it to the new location. You can also adjust the size and position of highlights, [text boxes](https://pdf.net/blog/how-to-add-text-box-to-pdf), and stamps with a simple **drag-and-drop functionality**.

## How to Share PDF Annotations When Collaborating

To share PDF annotations when collaborating, you need to **share the document using pdf.net’s annotation tool**. Once you upload your file into our tool, it is securely stored on our servers, and you can easily send it to clients or peers.

After they sign up on our platform, they can annotate the PDF and leave comments, highlight text, or make suggestions without actually editing the document. Being able to share and collaborate on annotated PDFs can help teams streamline communication and reduce misunderstandings due to undocumented file changes.

> **Highlight, Annotate, and Share Your PDFs in Seconds**
> 
> Upload your file, mark key sections, and keep your documents clear and easy to review—no downloads needed.
> 
> [Try it out NOW](https://app.pdf.net/sign-up)

## Troubleshooting Common PDF Annotation Issues

![Troubleshooting Common PDF Annotation Issues](https://cdn.sanity.io/images/i16te7yp/production/3ea947f69d43925a268c27160a0296112770fe6d-1195x794.jpg?fit=max&auto=format)

When you annotate PDFs, you may encounter some common issues like incorrect placement, overlapping annotations, and annotations that won’t save, so **here’s how to troubleshoot them**:

### #1. Incorrect Annotation Placement

Annotating PDFs using a touchpad or a mouse can be tricky, and you can place the annotation in the wrong location by accident. Fortunately, this common issue has an equally common fix; just **erase the annotation you initially made**. Afterward, you can add a new one in the right place.

### #2. Annotation Not Saving

Some users find that their annotations disappear, and this issue is often caused by the file not saving properly after annotating the PDF. If you use an offline annotation tool, it’s important to **always save your changes and review all the annotations you made **before closing the file.

When you annotate PDFs online, your changes are automatically saved and you can review your file before closing to confirm whether all your annotations are on the document.

### #3. Overlapping Annotations

Having multiple highlights, comments, or sticky notes on a document can cause overlapping annotations and make it difficult for you or your collaborators to read the original text. This is especially common when **annotating a PDF that’s shared with several people**.

To avoid confusion and ensure that all annotations are readable, consider using a different color for each person and grouping all related comments in the same area. Also, some PDF tools allow you to temporarily hide some comments so you only see what you need.

## Customize and Polish Your PDF With pdf.net

![Customize and Polish Your PDF](https://cdn.sanity.io/images/i16te7yp/production/201e183405313d31ab04d049fa2ae24485ea2d2a-1879x834.png?fit=max&auto=format)

Aside from annotating your PDF, you can also use pdf.net to modify and polish it in various other ways. We’ve already mentioned the signing tool for stamps, but you can also add actual, legally-binding e-signatures to your document with it.

Furthermore, you can:

- Change and add text with our **Text editing **tool
- **[Merge](https://pdf.net/merge-pdf) **smaller PDFs or **split** larger ones
- **Rearrange **and organize pages in a more logical order
- **[Compress](https://pdf.net/compress-pdf) **the document to make it easy to share
- **Password-protect** PDFs to ensure privacy and [**unlock**](https://pdf.net/unlock-pdf) them to access their content

And the best part is that you don’t have to worry about the security of your files as you use our PDF editor. We use **secure [HTTPS encryption](https://www.cloudflare.com/learning/ssl/what-is-https/)** and store your documents on our servers temporarily; the moment you finish customizing, they are deleted.

## Final Thoughts

Now that you know how to annotate PDFs, you’ll have a much easier time collaborating with others or working with long and complicated documents. Leave comments, highlight the most important parts, or draw directly on the PDF; all this and more is possible with pdf.net.

## How to Annotate PDF FAQs

### #1. How do I annotate a PDF without Adobe?

To annotate a PDF without Adobe, you need **annotation tools like pdf.net **that allow you to add comments to a PDF without altering its content.

### #2. Can I annotate a PDF on my phone or tablet?

Yes, **you can annotate a PDF on your phone or tablet **using pdf.net’s online annotation tool. As pdf.net is cloud-based software, you can use our tool on any device as long as you have a stable internet connection.

### #3. How do I delete annotations in a PDF?

To delete annotations in a PDF, simply **upload the document** to an [online editor](https://pdf.net/blog/best-pdf-editors) like pdf.net, **select the annotations** you want to erase, and then click **Remove**. Afterward, you can download your modified file or make new annotations.

## Related Articles

[How to Add Text to PDF Online: A Quick and Secure Method](https://pdf.net/blog/how-to-add-text-to-pdf)

[How to Edit PDF Files on Your Mobile: Edit PDFs Anywhere](https://pdf.net/blog/how-to-edit-pdf-file-on-mobile)