What actually happens to your PDF when you upload it — three architectures, the privacy trade-offs of each, and how to tell which online tools are trustworthy.
Browser-only tools (like most of PDFWix) never upload your file. The PDF is parsed and rewritten in JavaScript on your device. The server only sees that you visited a page, not what you did with the tool.
Server tools upload, process and ideally delete within minutes. Your file briefly lives on someone else's disk. The risk is bounded by their retention policy, their access controls, and the trust you place in their staff.
Open browser DevTools (F12), switch to the Network tab, run the tool with a test PDF, and watch what gets sent. If a request body contains your file's bytes, it's a server tool. If only small JSON pings appear, it's browser-side.
PDFWix encourages this — try it on Merge PDF and you'll see no upload of file content. We document which of our tools are server-based on the /security page.
No published retention policy, no HTTPS, ads inside the result, requirement to install desktop software for an online job, or vague language about 'improving the service' using your file.
A particularly concerning pattern: 'free' tools that require you to sign up before downloading. Sign-up gates exist to harvest emails for re-marketing — and if they monetize your email, ask what else they monetize.
Tax returns, medical records, contracts with personally identifying information: prefer browser-only tools, or use offline software (Adobe Acrobat, Apple Preview, qpdf).
If you must use a server tool, redact identifiers with a permanent redaction tool first, then run the conversion on the sanitized version.
No. Browser-side tools execute JavaScript locally; the server only sees that you loaded the page. Network requests carrying file bytes are visible in DevTools.
Reputable services delete within 1 hour (PDFWix's standard for server tools). Less-reputable ones may retain indefinitely. Always check the privacy policy.
PDFs can contain JavaScript and embedded files that pose risk if opened in a vulnerable reader. Modern Chrome, Edge, Safari and Firefox sandbox PDFs safely. Avoid opening unknown PDFs in old desktop readers.