What "free online converter" usually means
The typical flow behind most PDF-to-Word sites is: you drop a file in, it's uploaded to their server, their software converts it there, and a few seconds later you get a download link. That's a perfectly normal way to build a web tool — browsers historically couldn't do heavy document processing on their own, so sending the file off to a server was the only option. Many of these services state they delete files after an hour, or that they don't read them. Whether that's true for any given tool comes down to trusting their word, since there's no way for you to verify it from the outside.
Why that's worth a moment's thought
Most documents people run through a converter are genuinely mundane — a flyer, a form, an old essay. But plenty aren't: payslips, tenancy agreements, medical letters, signed contracts, ID scans. None of that means a given free converter is doing anything wrong with your file. It just means "upload it to a server first" adds a step, and a party, between you and your document that a browser-only tool skips entirely.
How to tell if a tool is uploading your file
You don't have to take a site's word for it — this is checkable in a couple of minutes:
- Open your browser's dev tools before you convert. In Chrome or Firefox, press F12, open the Network tab, then pick your PDF. If the tool uploads it, you'll see a request (usually a POST) carrying a file roughly the size of your PDF, headed to their server, within a second or two of picking it.
- Watch the UI language. Wording like "uploading…" or a progress bar that appears the instant you select a file (before any actual conversion could have started) is a strong sign the file is leaving your device first.
- Try it with your network disconnected. Load the page fully, then turn off Wi-Fi and mobile data, and try converting a file. A tool that keeps working with no network connection at all cannot be sending your file anywhere — there's nowhere for it to go.
How Altto does it differently
This tool reads your PDF using pdf.js — the same open-source engine Firefox and Chromium use to display PDFs natively — running directly inside the browser tab. It then builds the .docx file with a second in-browser library, docx.js, also entirely on your device. At no point does the file, or anything extracted from it, get sent to a server: there isn't a server in this tool's conversion path at all. You can confirm that yourself with the network-tab or offline checks above — after the page has finished loading, converting a file with your connection switched off works exactly the same as with it on.
The trade-offs of converting in the browser
Browser-only conversion isn't free of downsides, and it's worth knowing them:
- It uses your device's own processing power. A large file — many hundreds of pages, or tens of megabytes — will be slower than on a server farm built for exactly that workload, because it's your laptop or phone doing the work, not a data centre.
- No OCR. Reading text straight out of a PDF is lightweight enough to do locally; running optical character recognition on scanned image pages is a much heavier job that (for now) needs server-side compute, which is exactly the trade-off a browser-only tool is opting out of.
- It needs a reasonably modern browser. The libraries this relies on are standard in any current version of Chrome, Firefox, Edge, or Safari, but won't run on very old or unusual browsers.
For everyday documents — the kind most people are actually converting — none of that tends to matter in practice.
Related: even a password-protected PDF can be unlocked and converted the same way — the password stays on your device too.
See it for yourself
Drop a PDF in, and check your browser's network tab (or switch off Wi-Fi) while it converts — nothing leaves your device.