PdfMaster: Building a Zero-Upload Client-Side PDF Editor with pdf.js, pdf-lib, and Zustand

Almost every "free online PDF editor" follows the same dark pattern: you upload a sensitive contract or financial statement to a remote server, spend ten minutes annotating or reordering pages, and hit a paywall modal demanding a monthly subscription just to download your own file.

I built PdfMaster (PDF Editor Pro) to provide a zero-upload, privacy-first PDF editing suite that runs 100% client-side inside the browser—capable of rendering, searching, annotating, reordering, and exporting multi-page PDF documents without a single byte leaving your device.

Click to zoomPdfMaster Interactive Document Editor with live multi-page PDF rendering

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Dual-Engine Browser Architecture: pdf.js + pdf-lib#

A browser-native PDF editor has to solve two fundamentally different problems: high-DPI visual rendering and lossless binary PDF mutation. PdfMaster separates these responsibilities across two specialized engines coordinated by Zustand state stores (documentStore.ts and historyStore.ts):

1. Viewport Rendering & Full-Text Search (pdfjs-dist):
   • Renders each page onto hardware-accelerated HTML5 canvases with crisp zoom scaling, lazy viewport virtualization, and a live thumbnail strip (PageSidebar).
   • Extracts text layer geometry so pressing Ctrl+F (SearchPanel.tsx) highlights and jumps across matches instantaneously across hundreds of pages.
2. Binary AST Manipulation (pdf-lib):
   • When pages are reordered (@hello-pangea/dnd), rotated, deleted, or merged with another uploaded PDF, or when vector text and annotations are committed, pdf-lib mutates the underlying PDF object tree directly in memory and serializes a clean binary .pdf download.

Click to zoomPdfMaster Landing Page & Feature Overview

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Desktop & Mobile Ergonomics#

PdfMaster was designed to feel like a native desktop utility while remaining fully usable on tablets and phones:

• Command History (Ctrl+Z / Ctrl+Y): Full undo/redo stack (useHistoryStore) tracking page order permutations and annotation edits.
• Resizable Split Panels & Dark Mode: Drag-resizable sidebars, keyboard navigation (PageUp/PageDown, +/- zoom), and adaptive mobile toolbars (MobileToolbar.tsx).

The full source code is available on GitHub at daniazar/PdfMaster.