Merging a PDF, turning a contract into an image or converting a photo of your ID seems like a harmless task. But on many conversion sites, to do it, your file travels to someone else's server. It's worth knowing what that means.

Two ways to convert a file

On a server. Your file is uploaded, the site processes it on its own machines and sends the result back. For a while, a copy sits somewhere you don't control.

On your device. The site downloads the program to your browser and the file is processed right there. Nothing is sent. This is the method this site's tools use.

What can go wrong with server-side conversion

  • Retention. Some services keep files for hours, days or longer, and they don't always say so clearly.
  • Security breaches. A server with thousands of documents is an attractive target.
  • Use of data. Some sites' privacy policies allow the information to be used for other purposes.
  • Sensitive documents. Contracts, bank statements, IDs, medical prescriptions, schoolwork or client information shouldn't pass through third parties unnecessarily.

How to tell if a tool is private

  1. Read the privacy policy. It should clearly say whether files are uploaded and how long they're kept.
  2. Try the airplane mode test. Open the tool, disconnect your internet and try the conversion again. If it works, the file is processed on your device. If it asks for a connection or keeps loading, it's sending the file to a server.
  3. Watch the progress bar. If you see "uploading" with a time that depends on the file size, your file is traveling.

When it doesn't matter as much

For a public document, an image with no personal data or a file that's already on the internet, a server-based service is reasonable. Local conversion matters when the file contains information you don't want to share.

Good practices

  • Prefer tools that process on your device for sensitive documents.
  • Remove the pages you don't need before sharing a PDF; with split PDF you can extract only the ones you do.
  • Don't upload ID documents to services you don't know.
  • If a service offers "delete my file," use it as soon as you're done.

You can check how our merge PDF tool works: once the page has loaded, it works even offline.