Converting files privately: what "in your browser" really means — and how to check it
Many online converters upload your file to a server you know nothing about. The difference between uploading and converting in the browser, and a simple test anyone can do to see which one a site uses.
Two ways an online converter can work
Most online converters work on a server: your file travels over the internet to their computer, is converted there, and the result is sent back. For as long as it takes — and sometimes longer — a copy of your file exists on a computer you do not control, possibly in another country, possibly in logs and backups.
A converter that works in your browser does the opposite. When you open the page, your browser downloads a small program (JavaScript or WebAssembly) and runs it on your own device. The file is read and converted right there, and it never leaves your computer or phone.
Why it matters
- Confidential documents. Contracts, payslips, medical letters, identity documents, drawings under NDA — files you would not email to a stranger.
- Personal data of others. Under the GDPR, uploading a document with customers' or employees' personal data to a third-party service is processing by that service, with everything that entails.
- Company policy. Many employers forbid uploading work files to unknown websites — for good reasons.
- Speed. A large file converted locally does not have to be uploaded and downloaded first.
How to check it yourself
You do not have to take any website's word for it. Two simple tests:
- Watch the network. In Chrome, Edge or Firefox, press F12 and open the "Network" tab, then convert a file. If you see a request about as large as your file going out, it was uploaded. If only small requests appear, it was not.
- Pull the plug. Open the converter, then switch off your internet connection (airplane mode, or unplug the cable) and convert a file. If it still works, the conversion runs on your device. Some tools download a reading model or engine the first time; load them once while online, then try again offline.
What Convertburda does
Most of our tools run entirely in your browser — for example PDF to Word, merging PDFs, the image compressor and the EXIF remover. Try the offline test on them.
A few conversions genuinely need a server, because they depend on heavy engines that cannot run in a browser — for example Word and Excel to PDF, DWG drawings and e-invoices. Those tools say so on their own page. On our servers, which are in the EU, a file is processed in temporary storage and deleted as soon as the conversion is done; it is not kept, not logged by name and not used for anything else. You do not need an account for any of it.
One thing we add, and say openly: files you create here carry a short "made with convertburda.com" note in their metadata. It is invisible in the document itself, and it does not contain anything about you.
A server is not wrong — silence is
Converting on a server is not bad in itself. Some jobs simply need it: reproducing a Word layout exactly takes a complete office engine, and reading AutoCAD drawings takes specialised software that does not exist for browsers. What matters is that the site tells you which tools use a server, keeps the file no longer than the conversion takes, and runs its servers where your data protection law applies.
Be more careful with converter apps and browser extensions you install. An installed program or extension can read far more than the single file you give it, and a "free" one has to earn its money somewhere. A website that converts in the browser needs no installation and no permissions at all.
What to look for in any converter
- A clear statement of where files are processed — in the browser or on a server, and in which country.
- For server tools, how long files are kept, and whether they are used for anything else.
- Whether you need an account — for a one-off conversion you should not.
- Who runs the site: a real company, with contact details and a privacy policy you can read.
- Whether the files you get back contain more than you expect, such as hidden metadata.
Photos deserve a special mention: the file you share may carry the GPS location where it was taken. More about that, and about the other image formats, in our guide JPG, PNG, WebP, AVIF or HEIC.