rewirepdf

rewirepdf is a working fork of Mozilla's PDF.js focused on native PDF editing in the browser.

PDF.js remains the foundation for parsing, rendering, text layers, annotations, printing, and viewer behavior. rewirepdf extends that engine with experimental editing internals and a product shell in viewer-next/.

Why This Fork Exists

Editing existing PDF content cannot be solved cleanly from a product shell alone. A real editor needs access to the same facts PDF.js uses to parse, evaluate, render, select, and track document state.

This fork exists because rewirepdf modifies PDF.js internals to support native, source-based editing. The goal is to edit the original PDF content when it is safe to do so, instead of simulating edits with white boxes, overlays, or external conversion pipelines.

Native Source Text Editing

rewirepdf currently includes an experimental native source text editing pipeline.

The pipeline:

• preserves source references while PDF.js parses and evaluates text;
• exposes editable metadata through the text layer;
• maps visible text back to PDF content stream operators;
• validates replacements against the original source text, font encoding, operator fingerprints, layout policy, and target freshness;
• rewrites content streams conservatively through token-level filters;
• saves changes through incremental PDF updates.

This path is intentionally conservative. When PDF.js cannot prove that an edit is safe, it should return unsupported with useful diagnostics rather than guessing.

Important edge cases include text whose visible spacing comes from TJ spacing numbers, page /Contents arrays, Form XObjects, shared resources, annotation appearance streams, Type3 charprocs, and stale writer targets.

Architecture Rules

• Keep native editing logic close to PDF.js core/display/viewer internals when it depends on parsing, evaluation, layout, fonts, operators, or incremental save behavior.
• Keep application workflow, policy, and UI in viewer-next/.
• Do not require qpdf WASM, QDF as an intermediate format, external textual patches, or visual whiteout/overlay tricks for native source text editing.
• Keep unsupported cases structural and diagnosable.
• Keep the classic PDF.js viewer available and avoid product-specific rewrites of unrelated upstream behavior.

Viewer Next

The rewirepdf product shell lives in viewer-next/. It is a React/Vite interface that uses PDF.js through the local viewer-core boundary.

Useful entry points:

web/viewer.html?ui=next
build/generic/viewer-next/index.html

Development

From this repository root:

npm install
npm run viewer-next:dev -- --host 127.0.0.1
npm run viewer-next:build
npm run viewer-next:smoke

Use npm run viewer-next:build for general Viewer Next and integration changes. Use npm run viewer-next:smoke for upload, rendering, navigation, or PDF viewer behavior changes.

The underlying PDF.js generic build is still available through the usual gulp tasks, for example:

npx gulp generic
npx gulp server

Status

rewirepdf is experimental. The native editing work is active, browser-based, and intended to remain conservative: correctness and explicit diagnostics matter more than pretending every PDF is editable.

This repository is a fork of Mozilla PDF.js. PDF.js is developed and maintained by Mozilla and its contributors; rewirepdf builds on that work.