PDF Glossary

This glossary contains 27 PDF-related terms organized into 6 categories. Each definition is concise, factual, and includes related tools available in iReadPDF. Use this reference to understand PDF concepts, features, and technical terminology.

Updated: January 2026Version: 1.0

PDF Basics

PDF: Portable Document Format (PDF) is a file format developed by Adobe that preserves document formatting across different devices and operating systems. PDFs can contain text, images, hyperlinks, and interactive elements.
PDF/A: PDF/A is an ISO-standardized version of PDF designed for long-term archiving of electronic documents. It ensures documents remain viewable and reproducible indefinitely.
PDF/X: PDF/X is a subset of the PDF standard designed for graphic content exchange in printing and publishing. It ensures reliable reproduction of documents in professional print environments.
Page Size: Page size refers to the dimensions of a PDF page, commonly measured in inches or millimeters. Standard sizes include Letter (8.5x11 inches), A4 (210x297mm), and Legal (8.5x14 inches).

Conversion & OCR

OCR: Optical Character Recognition (OCR) is technology that converts images of text (such as scanned documents or photos) into machine-readable and searchable text. OCR enables editing and searching within scanned PDFs.
Rasterization: Rasterization is the process of converting vector graphics and text into a fixed-resolution image (raster). When converting PDF to image formats like PNG or JPEG, rasterization determines the output quality.
DPI: Dots Per Inch (DPI) measures the resolution of an image or scan. Higher DPI values (300+) produce sharper images suitable for printing, while lower values (72-150) are sufficient for screen viewing.
Flattening: Flattening a PDF merges all layers, annotations, and form fields into a single layer. This converts interactive elements into static content and reduces file complexity.

Security & Privacy

PDF Encryption: PDF encryption protects document contents using cryptographic algorithms (AES-128 or AES-256). Encrypted PDFs require a password to open or may restrict actions like printing, editing, or copying.
Digital Signature: A digital signature is a cryptographic mechanism that verifies the authenticity and integrity of a PDF document. It confirms the signer's identity and ensures the document has not been altered after signing.
Redaction: Redaction permanently removes sensitive information from a PDF by replacing text or images with black boxes. Unlike hiding or covering, properly redacted content cannot be recovered.
PDF Permissions: PDF permissions control what actions users can perform on a document, such as printing, editing, copying text, or adding annotations. Permissions are enforced through PDF security settings.
PDF Sanitization: PDF sanitization removes hidden data, metadata, embedded scripts, and potential security threats from a document. This process ensures PDFs are safe to share without leaking sensitive information.

Editing & Markup

Annotations: Annotations are comments, highlights, notes, or markup added to a PDF without modifying the original content. Common annotation types include sticky notes, text highlights, underlines, and freehand drawings.
Watermark: A watermark is text or an image overlaid on PDF pages, typically used for branding, copyright protection, or indicating document status (e.g., "Draft", "Confidential"). Watermarks can appear behind or in front of content.
PDF Metadata: PDF metadata is hidden information embedded in a document, including title, author, creation date, keywords, and application used. Metadata helps organize and search documents but may contain sensitive information.
Form Fields: Form fields are interactive elements in PDFs that allow users to enter data, such as text boxes, checkboxes, radio buttons, and dropdown menus. Fillable forms enable digital data collection.
Bookmarks: Bookmarks are a navigational feature in PDFs that create a clickable table of contents. They link to specific pages or sections, making it easier to navigate long documents.

AI Features

AI Summarization: AI summarization uses machine learning to automatically generate concise summaries of PDF content. It identifies key points, main ideas, and important sections without manual reading.
Intelligent Split: Intelligent split uses AI to automatically identify logical break points in a PDF based on content structure, chapters, or topics. It splits documents at meaningful boundaries rather than arbitrary page numbers.
Auto-Tagging: Auto-tagging uses AI to automatically add accessibility tags to PDF structure. Tags define reading order, headings, lists, and other elements, making documents accessible to screen readers.
Smart Redaction: Smart redaction uses AI to automatically detect and redact sensitive information such as names, addresses, social security numbers, and financial data from PDFs.

Technical Concepts

PDF Compression: PDF compression reduces file size by optimizing images, removing redundant data, and applying compression algorithms. Compression balances file size against quality for faster sharing and storage.
Linearization: Linearization (also called "Fast Web View") optimizes a PDF for quick display in web browsers. Linearized PDFs load the first page immediately while the rest downloads in the background.
Embedded Fonts: Embedded fonts are font files included within a PDF to ensure text displays correctly on any device. Embedding fonts preserves document appearance but increases file size.
PDF Layers: PDF layers (Optional Content Groups) allow different content to be shown or hidden within a single document. Common uses include showing/hiding annotations, language versions, or design variations.
PDF JavaScript: PDF JavaScript enables interactive features like form validation, calculations, and navigation within PDFs. However, JavaScript can pose security risks and is often disabled in PDF readers.

How we create definitions

Research industry-standard terminology from PDF specification documents
Verify accuracy against Adobe PDF Reference and ISO standards
Simplify technical language for general understanding
Link to related iReadPDF tools for practical application
Review and update quarterly or when standards change

Sources: Adobe PDF Reference, ISO 32000-2, W3C Accessibility Guidelines

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