cosmic-pdf

Cosmic PDF

Simplified Chinese

Cosmic PDF is a Chrome extension for reading PDFs in dark mode, with local text recognition, AI explanations, and a customizable reading experience.

PDF dark mode

Read PDFs with dark pages and a dark viewer background, including scanned documents. Switch to light mode whenever you prefer, without changing the original file.

The reader uses its own extension page to avoid a second dark-mode treatment by website extensions.

Reading tools

Open PDF links directly in Cosmic PDF, or choose a local file. Search text, navigate pages and outlines, adjust zoom, rotate left, enter full screen, print or download the original. You can also return to Chrome’s PDF reader.

Local OCR

Recognize scanned pages in English, Simplified Chinese or Traditional Chinese, including mixed Chinese and English. Select and copy recognized text directly on each page as recognition finishes. Recognition starts only when requested and does not upload or modify the PDF.

Explain with AI

Select a passage to clarify its meaning or ask a follow-up question. Choose Built-in AI via API for answers inside Cosmic PDF using your own Google Gemini, OpenAI or Claude API key, or Bring Your Own AI via Subscription to use your existing ChatGPT or Claude website account without an API key. The website opens beside the PDF where supported, otherwise in the next tab. The sparkle switch controls the selection button. Only your chosen text and nearby context when enabled are passed along.

Make it yours

Settings cover appearance, toolbar layout, 1×–6× rendering quality, optional sharpening, initial zoom, page spacing, thumbnails, document links, external-link capture and OCR preferences. The interface supports English and Simplified Chinese.

Install

Requires Chrome 128 or later. Download the installation ZIP, then unzip it. The complete source package is available separately.

  1. Open chrome://extensions and enable Developer mode.
  2. Choose Load unpacked and select the extension directory inside the unzipped package (or this repository).
  3. Pin Cosmic PDF if you want quick access to the file picker. Settings are available from the reader or the extension’s options menu.

To open file:// PDF links automatically, enable Allow access to file URLs in Chrome’s extension details, then reopen the extension or its Settings. Selecting or dropping a file works without that permission.

Automatic opening covers ordinary top-level HTTP(S) PDF responses and permitted local PDF links. Embedded readers, POST-generated documents and opaque blob links are not automatically replaced. Downloads marked as attachments retain normal download behavior. Some authenticated or single-use links may need Chrome’s reader or a local copy. Files larger than 64 MB remain outside this reader’s safety limit.

Privacy and safety

PDF reading and OCR run on this device. Documents, recognition results and built-in AI conversations stay in the open reader and are discarded when it closes; requesting an AI explanation sends the chosen text to your selected service. Website-mode conversations stay on the AI website, and their prefilled questions may appear in browser history or sync. Preferences and encrypted API keys are stored locally. Saved keys are listed by service in Settings, with individual test, replace and delete controls. AI availability, costs and data handling follow the selected provider’s terms. PDF scripting, form execution, editing and remote document resources are disabled. The original file is unchanged. No parser can guarantee safety against every malformed file; keep Chrome and the extension up to date.

Development

Run npm test and npm run check. Before publishing an update, run python3 scripts/build-downloads.py and commit the regenerated downloads/ files with the release. See technical documentation, browser QA and licenses and notices bundled under extension/vendor/.