> 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/ios/low-level-pdf-api.md). # Low-level PDF API - [Low-Level document editing (COS/SDF API) on iOS](https://docs.apryse.com/ios/low-level-pdf-api/low-level.md): Discover the power of low-level PDF APIs with Apryse SDK. Gain full access to COS/SDF object model, seamless integration, and unique functionalities for customizing PDF documents. Get started today! T - [Information dictionary: adding custom data to a PDF on iOS](https://docs.apryse.com/ios/low-level-pdf-api/add-custom.md): Learn how to add custom data to PDF files using the Cos/SDF low-level API with a full code sample. Edit existing documents easily with this comprehensive guide. The Apryse iOS SDK streamlines secure d - [Introduction to PDF file format](https://docs.apryse.com/ios/low-level-pdf-api/pdf.md): Learn about the basic structure of a PDF document, including header, body, cross-reference table, and trailer. Explore a simple "Hello World" PDF example and understand how objects are interconnected - [SDF / COS object model](https://docs.apryse.com/ios/low-level-pdf-api/sdf.md): Explore the complexities of real-life PDF documents and how to navigate them with Apryse CosEdit. Edit PDFs at the object level with ease using Apryse SDK's SDF/COS API. Learn more about the low-level - [Filters and streams on iOS](https://docs.apryse.com/ios/low-level-pdf-api/filters.md): Learn about SDF stream objects in PDF documents and how Apryse SDK efficiently processes streams using filter pipelines. Explore the Filter interface and MappedFile filter for enhanced performance. Ac - [Sample for editing PDFs using basic Cos/SDF API on iOS](https://docs.apryse.com/ios/low-level-pdf-api/samples.md): Unlock the power of Cos/SDF low-level API to edit PDF files with this informative sample. Learn how to manipulate existing documents effortlessly. The Apryse iOS SDK streamlines secure document proces - [APIs for low-level PDF document editing on iOS](https://docs.apryse.com/ios/low-level-pdf-api/apis.md): Discover utility classes for PDF documents in iOS using Objective-C and Swift. Explore the low-level API with PTObj and PTSDFDoc. Optimize your PDF workflow now! The Apryse iOS SDK streamlines secure --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://docs.apryse.com/ios/low-level-pdf-api.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.