Lumen – Offline PDF Search

Find any word inside any PDF on your phone — instantly, and completely offline.

Lumen is a privacy-first PDF search app. Point it at a folder of PDFs and it builds a full-text search index right on your device. Search for a word or phrase and Lumen shows you every match: the file name, the exact page number, and a highlighted snippet of the surrounding text. Tap a result to jump straight to that page.

No internet. No accounts. No tracking. Lumen has NO internet permission at all — your documents and your searches never leave your phone.

— WHY LUMEN —

• Full-text PDF search — search the contents of your PDFs, not just file names
• Find text in scanned PDFs — built-in offline OCR reads scanned and image-only documents so you can search them too
• Jump to the exact page — every result links to the page and highlights the match inside the built-in PDF viewer
• 100% offline — works on a plane, in a basement, anywhere, with zero signal
• Truly private — no internet permission, no analytics, no ads, no data
collection of any kind
• Fast — results appear as you type, even across hundreds of documents
• Lightweight on storage — Lumen never copies your PDFs; it reads them in place

— HOW IT WORKS —

1. Pick a folder of PDFs (Storage Access Framework — your files stay where they are)
2. Lumen indexes the text on every page in the background
3. Search any word or phrase and get filename + page number + highlighted
snippet results
4. Tap to open the PDF at the right page with the match highlighted

— PERFECT FOR —

• Students searching lecture notes, textbooks, and research papers
• Lawyers and paralegals searching contracts and case files
• Researchers and academics searching journal articles
• Anyone with a phone full of receipts, manuals, statements, or scanned docs

— PRIVACY YOU CAN VERIFY —

Lumen ships with NO internet permission — you can confirm this in the app's built-in Privacy Audit screen and in the app's permissions on Google Play. No Firebase, no analytics SDKs, no crash reporting, no advertising. Your search index lives in a local database on your device and nowhere else. Delete it any time from Settings.

Lumen is open source. Source code: github.com/royalgillz/Lumen

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