---
title: "Add comments to PDFs on web and mobile | Nutrient SDK"
canonical_url: "https://www.nutrient.io/guides/document-engine/instant-synchronization/comments/"
md_url: "https://www.nutrient.io/guides/document-engine/instant-synchronization/comments.md"
last_updated: "2026-06-08T17:11:05.481Z"
description: "This guide outlines everything you need to know about adding comments to PDFs on web and mobile. for Nutrient Document Engine SDK."
---

# Adding comments to PDFs on web and mobile

This guide outlines everything you need to know about adding comments to PDFs on web and mobile.

## Licensing

Comments require a separate component in your Nutrient license. Without this included in your license, you won’t be able to add the functionality of viewing, searching, or adding comments in your application. [Contact our Sales team](https://www.nutrient.io/contact-sales) to add comments to your license.

If you’re a new customer, you can [try comments](https://www.nutrient.io/demo/instant-collaboration/) without a license key. If you’re an existing customer, ask our [Sales team](https://www.nutrient.io/contact-sales) for a trial license if you’re interested.

## Terminology

Before starting, here are a few key terms related to comments:

- **Root annotation** — The annotation to which all the comments in a single thread are linked.

- **Comment thread** — A group of comments associated with the same root annotation.

- **Comment** — A single comment added by a user.

### Root annotation types

All comments are linked to their respective root annotations. The comments with the same root annotation are part of a single comment thread. There can be two types of root annotations:

## Getting started

## Adding a comment

You can add comments in two ways, depending on the type of root annotation.

At the moment, we don’t support the addition of comments or comment marker annotations using programmatic APIs. This is something that might change in the future.

## Deleting a comment

Comment editing isn’t supported in the current version.

## Supported platforms

Comments are supported on various platforms using Nutrient’s SDKs. Learn more by following the links below:

**[Instant Comments on iOS](https://www.nutrient.io/guides/ios/comments/introduction-to-instant-comments.md)**\
Use Instant Comments in your iOS applications

**[Instant Comments on Android](https://www.nutrient.io/guides/android/comments/introduction-to-instant-comments.md)**\
Use Instant Comments in your Android applications

**[Instant Comments on Web](https://www.nutrient.io/guides/web/annotations/comments-and-replies/comments.md)**\
Use Instant Comments in your web (browser-based) applications

**[Instant Comments on Flutter](https://www.nutrient.io/guides/flutter/instant-synchronization/comments.md)**\
Use Instant Comments in your Flutter applications

**[Instant Comments on React Native](https://www.nutrient.io/guides/react-native/instant-synchronization/comments.md)**\
Use Instant Comments in your React Native applications
---

## Related pages

- [Choose the right collaboration and synchronization setup](/guides/document-engine/instant-synchronization/choose-the-right-collaboration-and-synchronization-setup.md)
- [Integrate real-time collaboration with instant sync](/guides/document-engine/instant-synchronization/get-started.md)
- [Authenticate clients with JWT in Document Engine](/guides/document-engine/instant-synchronization/authentication.md)
- [Document layers for all workflows](/guides/document-engine/instant-synchronization/instant-layers.md)
- [Instant sync and real-time collaboration](/guides/document-engine/instant-synchronization.md)