PDF Forge LiB
PDF Forge LiB

PDF & image glossary

Plain-language definitions for the terms that come up across our tools and guides.

Base64

A way of representing binary data (like an image) as plain text, so it can be embedded directly in code such as CSS or HTML instead of linked as a separate file.

Convert an image to Base64

Bookmark (PDF)

A clickable entry in a PDF's navigation panel that jumps to a specific page or section - the PDF equivalent of a table of contents.

Color profile (RGB vs. CMYK)

RGB (red, green, blue) describes color for screens; CMYK (cyan, magenta, yellow, black) describes color for printing. A file designed for one can look noticeably different when used for the other.

Compression (lossy vs. lossless)

Lossy compression shrinks a file by discarding some detail (used by JPG and standard PDF compression); lossless compression shrinks it without losing any data (used by PNG). Lossy gets smaller; lossless stays exact.

Compress a PDF

Digital signature

A cryptographic mechanism that verifies who signed a document and confirms it hasn't been altered since - different from a simple scanned or drawn signature image.

Digital vs. electronic signatures explained

DPI (dots per inch)

A measure of image resolution - how many pixels are packed into each printed inch. 72-96 DPI is typical for screens; 300 DPI is the usual minimum for print.

Resize an image

Embedded font

A font file packaged directly inside a PDF, so the document displays with the correct typeface on any device - even one that doesn't have that font installed.

Encryption

Scrambling a file's contents so it can only be opened with the correct password or key - what actually secures a password-protected PDF, not just a surface-level lock.

Password-protect a PDF

EXIF data

Metadata a camera or phone embeds in a photo automatically - camera model, settings, timestamp, and sometimes GPS location. Invisible when you just look at the image.

How to view EXIF data in a photo

Favicon

The small icon shown in a browser tab, bookmarks bar, and history for a website - typically a 16x16 or 32x32 pixel image.

Generate a favicon

ICO file

A Windows/favicon icon format that can bundle multiple image sizes into a single file, letting the browser or OS pick whichever size fits.

Convert an image to ICO

Metadata

Data about a file, rather than its visible content - author, creation date, software used, camera settings, and so on. Often carried invisibly inside the file itself.

View an image's metadata

OCR (optical character recognition)

The process of recognizing text within a scanned image and adding it as a real, selectable, searchable text layer - without OCR, a scanned document is just a picture of text.

How OCR makes a scanned PDF searchable

PDF (Portable Document Format)

A file format built to look identical no matter what device or software opens it - fonts, layout, and images are all fixed into the file itself.

What is a PDF?

Permissions / owner password

A PDF password that restricts specific actions (printing, copying, editing) without requiring a password just to open and read the file - different from an open password, which blocks viewing entirely.

PDF passwords and permissions explained

Raster graphic

An image made of a fixed grid of pixels (JPG, PNG, WebP). Looks sharp at its native size but can blur or pixelate when scaled up significantly.

Convert between image formats

Rasterize / rasterization

Converting a vector graphic (built from mathematical shapes) into a fixed-pixel raster image - necessary for platforms that don't accept vector formats like SVG.

Convert SVG to PNG

Redaction

Permanently removing sensitive content from a document, not just visually covering it - a black box drawn over text without true redaction can often still be selected and copied out.

How to redact a PDF properly

Resolution

The pixel dimensions of an image (e.g. 1920x1080) - distinct from DPI, which describes pixel density when printed rather than the raw pixel count.

Resize an image

Thumbnail

A small, reduced-size preview of an image or document page, used for quick visual scanning without loading the full-resolution original.

Transparency / alpha channel

An extra channel of image data controlling how see-through each pixel is - what lets a logo sit cleanly on any background color. Supported by PNG and WebP; not by JPG.

Convert PNG to WebP

Vector graphic

An image built from mathematical shapes and paths (like SVG) rather than a fixed pixel grid - stays perfectly sharp at any size, which is why it's standard for logos and icons.

Convert SVG to PNG

Watermark

Text or an image overlaid across a document or photo, usually semi-transparent, to indicate ownership or discourage unauthorized use.

Add a watermark