Collate
A browser-based PDF workbench: combine any number of PDFs into one document, reorder pages across files with drag-and-drop, mark them up, and download the result. Everything runs client-side, so documents never touch a server.
Key features
- merge unlimited PDFs with page-level control in a thumbnail grid
- drag-and-drop page reordering across files, plus per-page deletion
- pen, highlighter, and text annotations with color options
- full-page preview with keyboard navigation
- handles XFA / Adobe LiveCycle forms that most web tools reject
- offline-capable: zero uploads, zero tracking
How it's built
Uses a dual-engine architecture: MuPDF compiled to WebAssembly handles parsing, rendering, and merging (including dynamic XFA forms that pdf-lib cannot parse), while pdf-lib stamps the annotation overlays onto the final document. Splitting the work this way gets the correctness of a real PDF engine with the ergonomics of a small JS library.