---
title: "Key annotation formats for PDF management"
canonical_url: "https://www.nutrient.io/guides/document-engine/annotations/introduction-to-annotations/data-formats/"
md_url: "https://www.nutrient.io/guides/document-engine/annotations/introduction-to-annotations/data-formats.md"
last_updated: "2026-05-14T16:53:43.808Z"
description: "Explore different annotation data formats like XFDF and Instant JSON for effective PDF management and synchronization across users and devices."
---

# Understand annotation data formats for PDFs

In addition to reading and writing annotations embedded into a PDF, Nutrient Document Engine enables you to use external files to manage annotations.![Separating annotations and form data from the underlying document](@/assets/guides/shared/annotations/separating-annotations-from-pdf-web.png)

Nutrient Document Engine supports reading and writing annotations in the following external data file formats:

- XML Forms Data Format (XFDF)

- Instant JSON

For most use cases, we recommend Instant JSON because, unlike XFDF, it can store deleted annotations. It also has build-in support for comparing (diffing) changes to annotations. This makes it ideal for synchronizing annotations to a server, or across users, devices, or sessions. XFDF is best suited for importing data into the system or exporting it for integration with third-party PDF applications.

## Comparing data formats

| Criteria                                     | XFDF    | Instant JSON |
| -------------------------------------------- | ------- | ------------ |
| Compatible with third-party PDF applications | ✓       |              |
| ISO-standard format                          | ✓       |              |
| Built-in support for comparing changes       |         | ✓            |
| Can store deleted annotations                |         | ✓            |
| Syntax                                       | Verbose | Minimal      |
| File size                                    | Larger  | Compact      |
| Fully documented                             | ✓       | ✓            |

## XML Forms Data Format (XFDF)

Nutrient Document Engine has full support for reading and writing XFDF.

XFDF is an XML-based standard from Adobe [XFDF (ISO 19444-1:2016)](https://www.iso.org/obp/ui/#iso:std:iso:19444:-1:ed-1:v1:en) for encoding annotations and form field values. It's compatible with Adobe Acrobat and many other third-party PDF applications.

XFDF is a representation of all annotation and form data inside a PDF document at a point in time. It doesn't have a concept of differentials (diffs) for managing changes made by multiple users annotating the same PDF simultaneously, and it cannot store deleted annotations. This makes XFDF a challenging format to use for comparing changes, managing conflicts, and synchronizing annotations across users, devices, or sessions.

## Instant JSON

Instant JSON is a format we created for bringing annotations and bookmarks into a modern format while keeping all important properties to make the Instant JSON spec work with PDF. It's not directly supported by other frameworks.

Instant JSON is [fully documented](https://www.nutrient.io/guides/document-engine/json.md) and supports persistent storage. It's designed for synchronizing annotations to a server, and across users, devices, or sessions.
---

## Related pages

- [Supported annotation types](/guides/document-engine/annotations/introduction-to-annotations/annotation-types.md)
- [Understanding PDF annotations and their types](/guides/document-engine/annotations/introduction-to-annotations/what-are-annotations.md)