Folio is a modern, lightweight web-based PDF viewer and annotation tool built with vanilla JavaScript. It allows users to open, view, zoom, annotate, and interact with PDF documents directly in the browser, no backend required.
- Load and render multi-page PDFs
- Smooth zoom in/out
- Page-by-page rendering
- Page number badges
- Thumbnail scaling support
- Loading overlay while rendering
- Freehand drawing
- Highlight tool (multiple color swatches)
- Text annotations (multi-line support)
- Stroke & fill customization
- Eraser tool
- Adjustable brush size & stroke width
- Custom annotation colors
- Undo / Redo support (per page)
- Snapshot-based state tracking
- Configurable history limit
- Light / Dark / System theme modes
- Custom accent color selection
- Persistent theme preferences (via
localStorage)
- Toast notifications
- Animated loading overlay
- Responsive layout
- Touch & mouse support
- Smooth scrolling
- Custom scrollbars
All dependencies are loaded via CDN — no build tools required.