Opening an EPUB or PDF in a reader app looks like a local operation. Often it is not. Conversion, text extraction, and “cloud sync” can all mean your file leaves the device, and the store listing rarely says so plainly.
Why a reading app would upload your book
Usually for a real engineering reason rather than a sinister one. Extracting text from a PDF is fiddly; doing it on a server is easier to build and easier to update. Sync across devices needs a copy somewhere. Neither is malicious. Both mean a copy of what you read exists off your device.
Whether that matters depends on what you read. For a public-domain novel, probably not. For a manuscript, a contract, a medical document or anything under NDA, it very much does.
How to tell before you trust it
- Turn off the network and open a book. The most direct test there is. If import fails in airplane mode, something is going out.
- Look for an account requirement. An app that must have a sign-in usually has a server holding something.
- Read the privacy policy for the word “process”. “We process your documents to provide the service” usually means upload.
- Check the store’s data-safety section. Both stores require a declaration; it is often more specific than the marketing.
What local-only means in practice
It means the file is read from device storage, parsed on the device, and the extracted text stored on the device. No account, no upload, no sync. The cost is real and worth stating: nothing is backed up, and your progress does not follow you to another phone.
That is the trade Punctum makes. There is no account, no server, and no mechanism by which a book could leave the device — which also means we cannot restore anything for you.
One current limitation, stated plainly
Scanned PDFs — pages that are images of text rather than text — are not supported. Handling them requires optical character recognition, and doing that well on-device is a different piece of work. Rather than import an empty book and let you discover it later, the app tells you at import time.
Related: speed reading apps compared.
References
- ScienceDirect — text presentation format and comprehension (karaoke > multi-line > single line > RSVP).