What you are actually sharing
A book file says something about you. The list of books you read reveals interests, health concerns, politics and plans. The file itself may carry metadata: your name if you edited it, a store account identifier in a bought copy, comments, or a library path in the file name. When a website converts a book on a server, all of that goes with it, and you rely on the operator’s promise about what happens next.
Local or server: how to tell
You do not have to trust a claim; you can test it.
- Open your browser’s developer tools (F12) and go to the Network tab.
- Choose your file in the tool.
- Look for a request with a large upload (a POST with a size close to the size of your book). If there is none, the file stayed in the browser.
- Even better: load the page, switch your device to airplane mode, and use the tool. A local tool keeps working.
On PDFSwift’s EPUB pages (reader, to-TXT, to-Markdown, text extractor, metadata editor, cover editor, validator, repair, merge and to-PDF) the processing code is a script loaded with the page, and you can confirm that no book is sent anywhere with the steps above. The pages do show third-party advertising; that code does not receive your files, and you can verify that in the same Network tab.
Where PDFSwift does use a server
PDFSwift also has an EPUB processing service for server-side operations, which is separate from the browser tools. It is intended for batch and programmatic use, requires a Pro entitlement for operations that change or convert books, does not store uploaded books, and processes them in memory. The tools on the site do not use it. If that ever changes, the page for the tool will say so before you choose a file.
What metadata leaks
| Where | What it can contain | What to do |
|---|---|---|
| Package metadata | Author, publisher, description, sometimes your own name | Check with the metadata editor before sharing. |
| File name | Store, account, source site | Rename before sending. |
| Identifier | ISBN or a per-purchase ID | Per-purchase IDs can tie a copy to a buyer; treat bought copies as personal. |
| Embedded files | Watermarks, tracking images fetched from the internet | The validator warns about remote resources. |
| Annotations | Highlights live in the reading app, usually not in the file | Export from the app deliberately. |
Habits that protect you
- Prefer tools that work in your browser or on your device, and verify with the Network tab once.
- Do not upload books that contain private information, such as a manuscript under contract, a medical document in EPUB form or an internal report, to a server you do not control.
- Read the tool’s retention statement, and be suspicious if there is none. “We delete files after an hour” still means they were stored for an hour.
- Be careful with tools that ask for an account for a one-off conversion; the account is a link between you and your library.
- Remember that advertising on a page is separate from the tool, but cookies and tracking affect your browsing. Use your browser’s privacy settings.
What local processing does not solve
A local tool keeps your book off other people’s servers; it does not make the output safe to share. The edited or converted file still carries whatever was in the original. Check metadata and file names before passing a book on, and only convert books you are allowed to convert.
A checklist for judging any online converter
| Question | Good sign | Warning sign |
|---|---|---|
| Where does processing happen? | Stated clearly: in your browser or on your device | No statement, or “secure cloud” only |
| Does the Network tab show an upload? | No request carrying your file | A large POST when you choose a file |
| Is there retention information? | Specific: “deleted immediately after processing” or “never stored” | None, or vague wording |
| Does it ask for an account? | No, for single conversions | Required before you can download |
| Does the result carry extra data? | Output identical in content, plain naming | Added watermark pages, links or tracking images |
| Who runs it? | Named company, contact address, privacy page | Anonymous site with many near-identical clones |
Different people, different risks
- Casual reader: the main risk is a profile of your reading habits and adware. Prefer local tools and ignore sites that insist on installs or extensions.
- Student or researcher: licensed material may have terms that forbid copying to third parties. A local tool avoids that question.
- Author or editor: unpublished manuscripts are valuable and sometimes under contract. Do not upload them to services you cannot verify, and strip metadata before sharing proofs.
- Organisation: internal documents in EPUB form fall under your data policies. Use tools that can run offline or inside your network.
Practical steps for PDFSwift’s tools
- Open the tool page and open your browser’s developer tools on the Network tab.
- Choose your book and run the tool.
- You will see page and script requests, and advertising requests. You will not see your book leaving.
- If you want to remove the advertising question entirely, switch to airplane mode after the page loads; the tool continues to work.