PDF Glossary

Your complete reference guide to PDF terminology, formats, and concepts. Whether you're a beginner or professional, this glossary explains the essential terms you need to understand PDF documents.

PDF Basics

PDF (Portable Document Format)

A file format developed by Adobe in 1993 designed to present documents independently of software, hardware, and operating systems. PDFs preserve formatting, fonts, images, and layout across all devices and platforms.

PDF Reader

Software application used to view, navigate, and interact with PDF files. Examples include Adobe Acrobat Reader, browser-based viewers, and operating system built-in PDF viewers.

Page Size

The dimensions of a PDF page, typically measured in inches or millimeters. Common page sizes include Letter (8.5" × 11"), A4 (210mm × 297mm), and Legal (8.5" × 14").

Metadata

Information about a PDF document stored within the file itself, including title, author, subject, keywords, creation date, modification date, and application used to create it.

PDF Standards & Formats

PDF/A (PDF for Archiving)

An ISO-standardized version of PDF designed for long-term archiving of electronic documents. PDF/A files are self-contained with all fonts and resources embedded, ensuring the document will display identically in the future.

PDF/X (PDF for eXchange)

A subset of PDF standards specifically for the graphic arts and printing industry. PDF/X ensures that files contain all necessary information for high-quality printing and color reproduction.

PDF/E (PDF for Engineering)

A PDF standard optimized for engineering workflows and technical documents, supporting 3D models, layered drawings, and specialized engineering content.

Tagged PDF

A PDF that includes structural information (tags) about the document's content, making it accessible to screen readers and assistive technologies. Essential for creating accessible documents for users with disabilities.

Compression & Optimization

Compression

The process of reducing PDF file size by removing redundant data or simplifying content. Can be lossless (perfect quality retained) or lossy (some quality trade-off for smaller size).

Lossless Compression

Compression that reduces file size without any quality loss. When decompressed, the file is identical to the original. Common lossless methods include Flate and LZW compression.

Lossy Compression

Compression that achieves higher compression ratios by permanently discarding some data. Results in smaller files but with some (usually imperceptible) quality loss. JPEG image compression in PDFs is lossy.

Downsampling

Reducing the resolution of images embedded in a PDF to decrease file size. For example, downsampling from 300 DPI to 150 DPI halves the image data while maintaining adequate quality for screen viewing.

DPI (Dots Per Inch)

A measurement of image resolution indicating how many dots of color appear in a linear inch. Higher DPI means more detail and larger file sizes. Typical values: 72 DPI for screen, 300 DPI for print.

Security & Protection

Encryption

The process of encoding a PDF's contents to prevent unauthorized access. PDF supports various encryption levels including 40-bit RC4 (weak), 128-bit AES, and 256-bit AES (strong).

User Password (Open Password)

A password that must be entered to open and view a PDF document. The PDF remains encrypted until the correct password is provided.

Owner Password (Permissions Password)

A password that controls what users can do with a PDF (print, copy, edit, etc.) even if they can open and view it. Used to protect copyright and maintain document integrity.

Digital Signature

A cryptographic signature applied to a PDF to verify the signer's identity and ensure the document hasn't been altered since signing. Provides authentication, integrity, and non-repudiation.

Certificate-Based Security

A security method using digital certificates to encrypt PDFs and verify identities. More secure than password-based protection for organizational use.

Conversion & Processing

Rasterization

Converting vector graphics or text into a bitmap image composed of pixels. Often used when converting PDFs to image formats like JPG or PNG.

Vectorization

The opposite of rasterization—converting bitmap images into vector graphics composed of mathematical paths. Produces scalable graphics that don't lose quality when enlarged.

OCR (Optical Character Recognition)

Technology that converts images of text (like scanned documents) into actual searchable and editable text. Makes image-based PDFs searchable and accessible.

Flattening

Converting all PDF layers, annotations, form fields, and transparency into a single, non-editable layer. Ensures consistent appearance but removes interactivity.

Linearization (Fast Web View)

Reorganizing a PDF's internal structure to allow page-by-page downloading from the web rather than requiring the entire file to download first. Enables faster viewing of large PDFs online.

Forms & Interactivity

Interactive Form (AcroForm)

A PDF containing fillable form fields like text boxes, checkboxes, radio buttons, and dropdown menus. Users can type information directly into the PDF.

Form Field

An interactive element in a PDF form where users can enter data. Types include text fields, checkboxes, radio buttons, dropdown lists, and signature fields.

JavaScript in PDF

PDFs can contain JavaScript code to add interactive features like form validation, calculations, and dynamic behavior. Poses potential security risks if from untrusted sources.

Annotation

Comments, highlights, notes, or markups added to a PDF without modifying the original content. Common annotation types include sticky notes, highlighting, and text comments.

Technical Concepts

Color Space

The color model used in a PDF document. Common color spaces include RGB (screen display), CMYK (printing), Grayscale (black and white tones), and Monochrome (pure black and white).

Font Embedding

Including the actual font files within a PDF to ensure text displays correctly even if the recipient doesn't have those fonts installed. Increases file size but guarantees consistent appearance.

Font Subsetting

Embedding only the specific characters used in a document rather than the entire font set. Reduces file size while maintaining visual fidelity.

Transparency

The ability for PDF elements to be partially see-through, allowing underlying content to show through. Can affect file size and printing compatibility.

Layer (Optional Content)

Separate levels of content in a PDF that can be shown or hidden independently. Useful for creating multilingual documents or documents with optional details.

Bookmark (Outline)

A navigation element in a PDF that creates a table of contents, allowing readers to jump directly to specific sections. Improves usability of long documents.

Hyperlink

A clickable link within a PDF that can navigate to other pages in the same document, other documents, or websites. Enhances document interactivity and navigation.

Client-Side Processing

Performing operations (like PDF conversion) directly in the user's web browser using JavaScript, without sending files to a server. Ensures privacy and faster processing.

Browser-Based Conversion

Converting PDFs entirely within a web browser using JavaScript libraries like PDF.js, jsPDF, and pdf-lib. Files never leave the user's device.

PDF.js

Mozilla's JavaScript library for rendering PDF documents in web browsers. Used in Firefox and many web applications for displaying PDFs without plugins.

Web Worker

A JavaScript feature that allows code to run in the background without freezing the user interface. Used for processing large PDFs without making the browser unresponsive.

Ready to Work with PDFs?

Use our free, browser-based PDF tools. Complete privacy guaranteed.

Try PDFormat Now →