What happens to a file on an ordinary converter site
When you drop a PDF onto most online converters, the first thing that happens is an upload. The file travels to a server somewhere, is converted there, and the result travels back. The site now has a copy of your document. What happens to that copy is described, if at all, in a privacy policy: many say files are deleted “after a few hours”, some keep them for days, some use them to train software, and a few have had their storage breached and the files leaked.
For a holiday photo this hardly matters. For a passport scan, a bank statement, a signed contract, a medical report, a payslip or a child’s school form, it matters a great deal, and most people never think about it because the page looks the same either way: a box, a button, a download.
There is another way to build these tools, and it is the way every tool on this site is built.
What “in your browser” means
A modern browser is a capable computer program. It can decode and re-encode images, read and write PDF and Word files, run compiled code at near-native speed through WebAssembly, and run machine-learning models on your device’s own processor and graphics chip. Everything a converter’s server does can be done on your side of the connection.
So when you choose a file on this site, the page reads it from your disk into the browser’s memory, does the work there, and offers you the result to save. The file is never sent to us or to anyone else. There is no server to send it to: the site is a set of static pages, and the only things that download from our servers are the pages themselves and, for the AI tools, the model files, which travel in one direction only, towards you.
This is not a privacy setting that could be switched off, or a promise that depends on a policy. It is how the tools are made. We could not read your files if we wanted to, because they never arrive.
A few consequences follow that are worth knowing:
- Large files are fine. There is no upload limit because there is no upload. The limit is your device’s memory, which for a phone means PDFs of a few hundred pages and photos of a few thousand pixels a side are comfortable.
- It keeps working offline once it has run. The first time you use a tool, it downloads the code it needs (and on the AI tools, the model). After that first job you can switch off Wi-Fi and mobile data, and it keeps working for as long as the page stays open. The browser keeps the model files for next time; the page itself still needs a connection to open.
- Speed depends on your device, not on our servers or on your connection. A laptop converts a long PDF in seconds; a five-year-old phone takes longer.
- Nothing is kept between visits unless you ask for it. The one exception is a signature you tick “remember on this device” for in the Sign PDF tool, which is stored in your browser’s local storage and can be removed in the signature window at any time.
How to check it yourself
You should not have to take this on trust, and you do not. Two checks take a minute.
The airplane-mode test. Open a tool and run it once on any file, so that it has everything it needs (on the AI tools, this also downloads the model). Then, with the page still open, turn on airplane mode (or unplug the network cable), choose your own file and run the tool again. If it works, the file cannot have gone anywhere, because there was nowhere for it to go.
The network tab. In a desktop browser, press F12 (or Cmd-Option-I on a Mac) and open the Network tab, then use the tool. Every request the page makes is listed, with its destination and size. You will see the page’s own files and model files coming from toolboxhere.
| Check | What you should see |
|---|---|
| Airplane mode after a first run, page still open | The tool still converts, compresses, reads or transcribes |
| Network tab while using a tool | Downloads from toolboxhere. |
| Size of outgoing requests | Bytes, not megabytes |
| Our own daily check | Automated tests load every tool on the live site each day and fail if any request goes to a server other than ours or Google’s analytics and advertising services |
That last row is how we check ourselves: the same test suite that runs before every change also runs against the live site daily, and one of its rules is that no request leaves for an unexpected destination.
Try it: ID Card to A4
Lay the front and back of an ID card on one page for printing or sending. The card images are read and placed on your device; make one PDF, then switch on airplane mode and make another.
What does leave your device, honestly
“Your files never leave your device” is a precise claim about your files. It is not a claim that the page makes no network requests at all, and we would rather you knew exactly what the others are.
Analytics. The pages load Google Analytics, which tells us how many people use each tool, on what kind of device, and how they found the site. It sets a first-party cookie to tell repeat visits apart. Google Analytics 4 does not log or store IP addresses, and we have advertising features, Google Signals and ad personalisation switched off. It never sees your files, your text or your results: the tools do not report what you did, only that a page was opened.
Advertising. The site is free and is paid for by advertising. Google’s advertising script loads on the pages and shows ads; like analytics, it knows which page you are on, not what you put into the tool. Visitors in Europe and the UK see a consent message first, and the “Privacy and cookie settings” link in the footer reopens it.
Hosting. The pages and model files are served by Cloudflare, which, like any web host, sees your IP address and browser type when it delivers them.
The phone link. Scan to PDF, ID Card to A4, Fill PDF Form and Sign PDF can link your phone to the page open on your computer by scanning a QR code, so pages photographed on the phone appear on the computer. The two browsers connect directly to each other where the network allows it. When it does not, the pages pass through a small relay service we run, encrypted on your phone with a key that is part of the QR code and is never sent to us; the relay forwards bytes it cannot read and stores nothing.
None of these carry the content of your files. If you would rather they did not run at all, the airplane-mode test above shows that the tools work without them.
Why this is the right way to build these tools
It would be easier to run the tools on a server. Server code is simpler to write, works on every device however old, and gives the site owner statistics about what people convert. We chose the other way for three reasons.
The first is the obvious one: the files people bring to tools like these are often the most sensitive documents they own, and the safest place for a sensitive document is the device it is already on.
The second is that it keeps the site honest. A privacy policy that says “we delete your files” asks you to trust a process you cannot see. A tool that never receives the file asks nothing of you, and you can verify it in a minute.
The third is cost, which is also why the site can stay free. Converting other people’s files on servers costs money for every file; running the work in your browser costs us nothing per file, so there is no reason to limit you to three conversions a day or to sell a “pro” tier for larger files.
If you ever find a request on this site that you cannot account for, tell us through the contact page; that is a bug, and we would want to fix it the same day.
Frequently asked questions
How can I be sure my file was not uploaded?
Run the tool once, then switch on airplane mode with the page still open and run it again on your file. If it still works, the file had nowhere to go. On a computer you can also open the browser’s Network tab (F12) and watch: the page downloads from toolboxhere.
Is there a file size limit?
No upload means no upload limit. The limit is your device’s memory: a laptop handles PDFs of hundreds of pages and photos of several thousand pixels a side; a phone is more constrained, and the tool tells you when a file is too large for it.
Does the site keep anything between visits?
Only what you ask it to. A signature you tick “remember on this device” for in Sign PDF is stored in your browser’s local storage, and the AI tools’ model files are cached by your browser so they do not download again. Both are on your device and can be cleared like any site data.
What does Google Analytics see?
That a page was opened, on what kind of device and how you arrived. It sets a first-party cookie to tell repeat visits apart, does not log IP addresses, and never sees your files, your text or your results; we have advertising features and Google Signals switched off.
Is the phone link private?
Yes. When you link your phone to the computer by QR code, the two browsers usually connect directly. If the network prevents that, the pages pass through our relay encrypted with a key that is part of the QR code and never sent to us; the relay forwards bytes it cannot read and stores nothing.
Written by Saad Naeem
AI engineer in Doha who builds every tool on ToolboxHere. The figures in the guides come from the official sources named in them or from the tools themselves. Found a mistake? Tell us and it is corrected.