We tested 15 online file tools: 14 uploaded our file
When you drop a file into a free online PDF, image or audio tool, does it stay on your computer – or is it sent to a server? We watched the network traffic of 15 popular tools to find out. 14 of them uploaded our test file, and 11 did so the moment we selected it, before we pressed any button.
Test run: 27 October 2026. Synthetic test files only – no personal data.
The results
| Tool | Task | Uploaded? | Sent to | When |
|---|---|---|---|---|
| iLovePDF | Compress PDF | Yes | api30.ilovepdf.com | On selecting the file |
| Smallpdf | Compress PDF | Yes | Cloudflare R2 storage bucket | On selecting the file |
| PDF24 Tools | Compress PDF | Yes | filetools19.pdf24.org | On selecting the file |
| Sejda | Compress PDF | Yes | sejda.com | On selecting the file |
| Adobe Acrobat online | Compress PDF | Yes | unity-an1.adobe.io | On selecting the file |
| PDF2Go | Compress PDF | Yes | www12.pdf2go.com | On selecting the file |
| TinyPNG | Compress PNG | Yes | tinypng.com | On selecting the file |
| iLoveIMG | Compress image | Yes | api33.iloveimg.com | On selecting the file |
| remove.bg | Remove background | Yes | remove.bg | On adding the file |
| Squoosh | Compress PNG | No | – | – |
| CloudConvert | PNG to JPG | Yes | eu-central.storage.cloudconvert.com | After clicking Convert |
| Convertio | PNG to JPG | Yes | s177.convertio.me | After clicking Convert |
| Zamzar | PNG to JPG | Yes | zamzar.com | After clicking Convert Now |
| 123apps Audio Joiner | Join two WAV files | Yes | s88.audio-joiner.com | On adding the files |
| Clideo | Merge audio | Yes | cs33 and cs65.clideo.com | On adding the files |
What we found
- 14 of 15 tools uploaded the whole file. Only Squoosh kept it on the device.
- 11 uploaded before we clicked anything. Choosing the file was enough – even if you change your mind and close the tab, the copy has already been sent.
- Three converters waited for a click. CloudConvert, Convertio and Zamzar only uploaded after we pressed Convert.
- “In your browser” did not mean on your device. PDF2Go’s compress page says “Reduce the file size of your PDF in your browser. Free, fast and private.” – and then showed “1 file uploaded” after sending the PDF to its server.
- Some sites say how long they keep files. Sejda states files are deleted after 2 hours; Convertio and Zamzar say converted files are stored for 24 hours; Adobe says the file is “securely handled by Adobe servers and deleted unless you sign in to save it.”
How we tested
We opened each tool in a Chromium browser, declined optional cookies where a banner offered it, and added a small script that records every outgoing request larger than 1 KB – its destination, path and size. Then we chose a synthetic test file in the tool’s own file picker: a one-page generated PDF (10,757 bytes), a generated image (26–565 KB) or a 10-second tone (882,044 bytes). A tool counts as uploading when a request at least as large as the file went to its server. Small analytics requests are not counted.
This shows where the file went, not what each company does with it afterwards. It is one run per tool from one location; websites change, and a tool may behave differently elsewhere or later.
Why it matters
Uploading is how most online tools work, and many delete files after a while. But a PDF of your passport, a contract or a bank statement is a copy you no longer control once it is on someone else’s server. Tools that run in the browser – using WebAssembly versions of the same libraries desktop apps use – can do most everyday jobs without that copy ever existing.
Tools that don’t upload
FilesProcess was our control: its PDF, image and audio tools process files on your device, and in this test only a 1 KB analytics request left the page. See how it works and check it yourself, or try Compress PDF, Compress Image and Merge Audio.
Frequently asked questions
Is it bad that online tools upload files?
Not in itself – many tools need a server, and several of those tested say they delete files after a few hours. But once a copy exists on someone else’s computer, you rely on their security and their word. For ID documents, contracts, medical records or anything confidential, a tool that never uploads removes that risk.
Do these tools keep my files?
This test shows where the file went, not what happened to it afterwards. Some sites state deletion times on the page: Sejda says files are deleted after 2 hours; Convertio and Zamzar say converted files are stored for 24 hours; Adobe says the file is deleted unless you sign in to save it.
How can I check a website myself?
Open the browser’s developer tools (F12, or right-click → Inspect), go to the Network tab, then choose a file in the tool. Look for POST or PUT requests whose size is about the size of your file. If one goes to a server while you are just selecting the file, it was uploaded.
Which tools did not upload?
Squoosh, Google’s open-source image compressor, processed the image in the browser. FilesProcess, which we tested as a control, did the same.
Will you repeat the test?
Yes. Websites change, so we plan to re-run it and update this page with the date of each run.
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