> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/core/low-level-pdf-api/low-level.md).

# Low-Level document editing (COS/SDF API) on Server/Desktop

Discover the benefits of working with low-level PDF APIs using Apryse SDK. Gain full access to COS/SDF object model, seamless integration, and unique functionalities for customizing PDF documents. Sta

Working with low-level PDF APIs can enable a wide variety of customizations with PDF documents.

Apryse SDK offers the following benefits:

* Full access to low-level PDF object model (also known as COS/SDF)
* Seamless integration between high and low-level API
* Functionality not available in the high-level API can be implemented using COS/SDF API

## Get started

[Adding custom information](/core/low-level-pdf-api/add-custom.md) To add custom information to an existing document.

[A short introduction to PDF file format](/core/low-level-pdf-api/pdf.md) An introduction to PDF file format.

[SDF / COS object model](/core/low-level-pdf-api/sdf.md) An introduction to SDF objects.

[Filters and streams](/core/low-level-pdf-api/filters.md) An introduction to filters and streams.

[Embedded Fonts](/core/basic-operations/extraction/embedded-fonts.md) An introduction to embedded fonts.

## Tools & utilities

[PDF CosEdit](/cli/pdf-cosedit/pdf-cosedit.md) A windows GUI tool for low-level PDF editing to view, add, or edit information for an existing document.


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