It depends on two things: whether your file goes to a server, and what's in it. Compressing a restaurant menu on any site is harmless; dropping a payslip, a bank statement or a passport scan on one leaves a copy with a third party for anything from a few seconds to twenty-four hours, depending on the site. The rule of thumb: anything you wouldn't publish, process with a tool that doesn't upload the file — and check that for yourself in thirty seconds.
Which document, which risk
| Document | Verdict | Why |
|---|---|---|
| Menu, poster, programme, anything already public, course notes | No concern | Nothing personal or confidential: a copy on a server changes nothing. |
| Quote, invoice, CV, commercial contract, internal report | Think first | Contact details, prices, margins, clients: nothing irreparable, but information a competitor or a fraudster would love to read. At work, it's also data leaving the company without IT knowing. |
| ID card, passport, driving licence | Don't upload | The raw material of identity theft. If you have to send one, watermark it first. |
| Tax documents | Don't upload | Income, address, tax reference; the French tax notice even carries a barcode that holds more than people think they've hidden (what to redact). |
| Bank statement, bank details, payslip | Don't upload | Salary, employer, account number, spending habits: everything needed for invoice fraud or tailor-made phishing. |
| Medical records, prescriptions, sick notes | Don't upload | Health data is the most protected category under the GDPR; PDF24, for one, makes the user "solely responsible" for processing doctor's letters on its site (PDF24 terms). |
"Don't upload" doesn't mean "don't convert": these documents are perfectly fine to process with a tool that works on your own computer.
The 30-second test: does the tool upload your file?
You don't have to take any site's word for it, ours included.
- The flight-mode test. Open the tool's page, give it a few seconds to finish loading, then switch off the Wi-Fi (or turn on flight mode). Drop a file and run the job. If the tool sends files to a server, it fails; if it works locally, it runs.
- The Network tab. More precise: open your browser's developer tools (F12, Network tab), drop a file and watch what goes out. A request of several megabytes to a server the moment you drop the file is your file.
On PDFKami, all nineteen tools pass the first test: each page downloads its processing engine just after it appears, and needs no network after that. Two honest caveats. The site doesn't install itself for offline use: once you've cut the connection, stay on the open page — don't reload it or switch to another tool. And if your browser is in data-saver mode, the engine only downloads when you drop your first file, so drop one before you disconnect.
The flight-mode test proves the processing is local; it doesn't prove a page won't send anything once you're back online. The Network tab shows that. On PDFKami, the page's security policy (CSP) blocks any connection to a site other than ours: that isn't a promise, it's a rule your browser enforces.
What happens when the file does go
On most online PDF tools:
- your browser uploads the whole file to the service's servers, usually at a cloud provider, sometimes outside Europe;
- the server processes it: merging, compressing, converting;
- the result is stored temporarily and you're handed a download link;
- the original and the result are deleted… eventually, depending on the service's policy.
The work isn't done "online"; it's done on their machines. Your browser is just the front desk.
The risk isn't theoretical. In July 2024, researchers at Cybernews found that two online converters owned by the same British company, PDF Pro and Help PDF, had left a storage area open to anyone, holding 89,000 documents uploaded by users: passports, driving licences, contracts (Cybernews). No hacking involved: one badly configured setting.
Our evidence: what we found
Almost every page that answers this question is written by an online PDF tool, and concludes that its own service is safe. We make a PDF tool too, so here's what we found, sourced, for you to check.
The ten most popular free PDF sites all upload your file. Our comparison looked at iLovePDF, Smallpdf, PDF24, Adobe, Sejda, PDF Candy, Soda PDF, PDF2Go, Convertio and Online2PDF: none documents any in-browser processing for its online tools. Stated retention runs from immediate deletion (Online2PDF) to twenty-four hours (Soda PDF, and Convertio for the converted file), via one hour (PDF24) and two hours (iLovePDF, Sejda, PDF Candy); Adobe and PDF2Go give no figure. On advertising, according to the WhoTracks.me observatory, Adobe shows 6.3 trackers per page (measured across the whole of adobe.com), and more than half the requests made by PDF24's pages (52%) are for tracking.
Three services read in detail.
- Smallpdf promises deletion "after one hour", but its privacy policy only commits to that for users with an account; and the file may pass through Cloudflare, "in the United States or in Europe".
- Adobe Acrobat online processes data mainly in the US and India, lists OpenAI and Google Gemini among its sub-processors, and switches machine-learning content analysis on by default for personal accounts.
- PDF24 processes files in the European Union and deletes them within the hour, but its terms make the user "solely responsible" for sensitive documents. Its Windows program, PDF24 Creator, does work locally.
The fake-converter risk. In March 2025, the FBI warned about conversion sites that deliver the file you asked for… with malware attached, and that trawl uploaded documents for personal data. One campaign documented since hit the UK (14% of victims) and France (9%) particularly hard (the FBI's warning, and how to spot these sites).
The questions to ask before you drop a file
Even with a reputable service — and plenty are — you're trusting it by default. Before uploading anything sensitive, you should be able to answer:
How long is the file kept? The answer is in the privacy policy, rarely on the tool's own page, and it sometimes depends on whether you have an account.
Where are the servers, and who runs them? For EU citizens' personal data, hosting outside the EU means a different legal regime. And an American provider, even with servers in Europe, is still subject to the CLOUD Act.
Who can get at it? The service's staff, its subcontractors, the hosting provider; and, after a leak, anyone.
Is the file analysed? Some services extract metadata, analyse content to "improve the service" or pass it to AI providers.
What are the adverts paying for? A free tool plastered with banners is monetising your visit, often through third-party trackers loaded on the very page where you drop your file.
Who this really matters to
- HR and payroll: payslips, employment contracts, sick notes.
- Legal and notarial work: deeds, court papers, documents bound by professional confidentiality.
- Healthcare: reports, prescriptions, scans.
- Finance and accounting: balance sheets, statements, tax returns.
- Any business: an employee who "quickly" compresses an internal report on a free site has just taken it outside the company perimeter.
- You, personally: ID, tax documents, proof of address — exactly what people convert for a rental application or a bit of admin.
The alternative: don't send the file
Rather than manage the risk, you can remove it: do the processing on your own computer, inside the browser. Modern browsers can merge, split, compress or convert a PDF locally, in JavaScript or WebAssembly. The page reads the file, transforms it in your machine's memory and hands you the result as a download, without a single byte going to a server.
That's how PDFKami works:
- No upload. There's nothing to delete server-side, because there's nothing server-side.
- Verifiable. The flight-mode test and the Network tab, described above, are all it takes.
- No cookies, no trackers, no adverts. No banner to click through.
- No account, no usage limits.
- Hosted in Europe. The site itself (the page — not your files, which never travel) is served from European infrastructure.
That covers the everyday jobs: merge PDFs, compress a PDF, split or reorder pages, turn images into a PDF, convert Word to PDF, convert Markdown to PDF, add page numbers, redact or password-protect a PDF.
Where the local approach falls short
Not everything can be done in a browser, and PDFKami doesn't do everything. It offers no optical character recognition (OCR), no PDF-to-Word conversion, and no advanced or qualified electronic signature: Edit PDF lets you draw your signature, but the result is the equivalent of a page signed and scanned, with no identification of the signer in the sense of the EU's eIDAS regulation. For those jobs, pick a service whose retention policy you've actually read, or install software on your own machine.
For everything else — which is most day-to-day PDF work — there's no longer any reason to send your files to anyone. Process them on PDFKami, right in your browser.