Tag

Internals

How the PDF format actually works underneath — object structure, content streams, filters, incremental updates, embedded files, and the specification details that explain otherwise baffling behaviour.

17 posts

PDF Metadata and XMP Explained

Every PDF carries metadata in at least two places, they frequently disagree, and most people editing a document's title are only changing one of them…

GuidesInternals

Aug 4, 2026·7 min read

How to Set the Initial View of a PDF

When someone opens your PDF, the viewer makes a series of decisions on your behalf: what zoom level, which page, whether the bookmarks panel is showing…

GuidesInternals

Jul 28, 2026·6 min read

How to Embed a PDF in a Web Page

Putting a PDF on a web page looks like a one-line job — and it is, if you accept whatever the visitor's browser decides to do with it. The differences between…

GuidesInternals

Jul 27, 2026·6 min read

PDF Page Labels Explained

Open a scanned book in a PDF viewer and you will often see something odd: the viewer says page 1 of 340, but the page in front of you is the cover, and the…

GuidesInternals

Jul 27, 2026·7 min read

PDF Portfolios Explained

A PDF Portfolio is a PDF whose job is to be a container: a single file that holds a set of other files — PDFs, spreadsheets, images, emails, videos — each kept…

GuidesInternals

Jul 27, 2026·6 min read

How to Split a PDF by Bookmarks

Splitting a PDF at fixed page intervals is easy and usually wrong. What you actually want, most of the time, is to split it at the structural boundaries — one…

GuidesInternals

Jul 26, 2026·6 min read

PDF Compression Filters Explained

A PDF is full of compressed content: page streams, embedded images, fonts, embedded files. The compression schemes are called "filters" in PDF terminology…

GuidesCompressionInternals

May 19, 2026·8 min read

PDF Incremental Updates Explained

When you save a PDF after editing, the writer can either rewrite the whole file or append a small update at the end. The second option, called an incremental…

GuidesInternals

May 18, 2026·7 min read

Digital Signature Internals in PDF

A digital signature on a PDF is more than a scribbled image. It's a cryptographic operation that proves who signed, when, and that the document hasn't been…

Security & PrivacySigningInternals

May 17, 2026·8 min read

PDF Attachments and Embedded Files

A PDF can carry other files inside it. The feature, called "file attachments" or "embedded files," has been in the PDF spec for two decades and powers…

GuidesInternals

May 16, 2026·7 min read

XFA Forms Explained

XFA (XML Forms Architecture) is the more powerful, more complex, and increasingly deprecated form technology in the PDF ecosystem. XFA forms support dynamic…

FormsFillable FormsInternals

May 15, 2026·7 min read

Embedded Video and Rich Media in PDFs

A PDF can contain video, audio, and other rich media. Hover over a still image in a marketing PDF and it plays a product demo; open a research paper and a…

GuidesInternals

May 14, 2026·7 min read

3D PDFs Explained

A PDF can contain a fully interactive 3D model: a CAD assembly, a molecular structure, a building model, a medical scan. Open the PDF, click the 3D area, and…

GuidesInternals

May 13, 2026·7 min read

Interactive PDFs With JavaScript

PDFs can run JavaScript. The feature has been in the spec for decades and powers everything from form validation to interactive scientific charts to malicious…

GuidesInternals

May 12, 2026·7 min read

PDF Internals: Objects and Streams

A PDF looks like a single document, but inside it is a small structured database of objects. Open a PDF in a hex editor or a text editor and you see a soup of…

GuidesInternals

May 11, 2026·8 min read

Multimodal LLMs and PDF Documents

The shift from text-only LLMs to multimodal models (text plus vision) has reshaped what AI can do with PDFs. A 2023 LLM had to depend on text extraction; if…

AIAIInternals

Apr 9, 2026·8 min read

Building a RAG System With PDF Knowledge Bases

Retrieval-augmented generation (RAG) is the dominant pattern for getting an LLM to answer questions over your own documents. PDFs are the most common source…

AIAIInternals

Apr 1, 2026·8 min read