Extend UI is an open source React component library designed for building robust document processing products and workflows. Developed by the team at Extend, the library provides a set of high-performance, production-ready front-end primitives specifically tailored for handling documents like PDFs, DOCX files, spreadsheets, and various text-based formats. The library helps development teams move from raw file handling to structured, validated data outputs by offering components for viewing, navigating, searching, and managing complex document assets. By leveraging shared controls for annotation, extraction, and validation, Extend UI enables developers to build interfaces where users can review AI-extracted content, resolve low-confidence fields, and perform human-in-the-loop document checks efficiently. The component set is built for scalability and is designed to integrate seamlessly into internal tools, user-facing document workflows, or agentic systems that require precise interaction with document layouts.

Some of the key features are:

• PDF Viewer: A professional-grade component featuring lazy page rendering, page navigation, zoom, rotation, and support for OCR overlays.
• Excel Viewer: An interactive spreadsheet viewer for XLSX files supporting sheet tabs, frozen panes, formula displays, and cell selection.
• Document Splits: A tool for managing large documents by organizing them into logical, editable groups via drag-and-drop interfaces.
• File System (Finder): A macOS-style file browser that handles flat object-store manifests with support for multiple views including icon, list, column, and gallery.
• File Upload: A flexible drag-and-drop component with built-in validation for file types, sizes, and batch processing.
• Schema Builder: A utility for creating and managing data extraction schemas within the document interface.
• E-Signature: A dedicated component for managing electronic signature workflows directly within the document viewing context.
• Bounding Box Citations: Specialized UI for highlighting extracted data areas directly on the source document.

Extend UI is designed to be highly modular, allowing developers to import specific components as needed while utilizing a standard React development flow. Components are maintained to work independently or in combination, such as pairing the Document Splits viewer with the main PDF component for an end-to-end file organization interface. The library also includes advanced layout blocks that assist in creating responsive dashboards for document-heavy applications. Implementation is straightforward, often requiring only a single command to add specific components into existing projects, following modern React best practices and providing a clean API surface for developers to hook into data processing pipelines and event triggers.

Some common use cases include:

• Financial Reporting: Building document-heavy portals for viewing and auditing financial PDFs and complex Excel models.
• Healthcare Processing: Creating internal review surfaces to validate patient records, scanned forms, and medical data extracted from diverse documents.
• Legal Document Management: Implementing secure environments for legal teams to review, split, annotate, and sign multi-page contracts and legal filings.
• Logistics Workflows: Developing tools for agents to parse shipping documents, invoices, and bills of lading at scale with human-in-the-loop oversight.