Did my file leave this computer?

Open the tool you are testing. Press F12 (or right-click, then Inspect), and switch to the Network tab. Leave it open. Now do the thing the tool is for — drop your PDF in, press convert. Watch the list that fills up.

If a request appears whose size is roughly the size of your file, your file was sent somewhere. That is the whole test. A 4 MB PDF shows up as a 4 MB upload; a 20 MB zip of photos shows up as a 20 MB upload. You do not need to understand the request, only compare the number.

What you are looking for

• A POST or PUT in the list, usually to an address that is not the site you are on.
• A size that matches your file. The Network tab has a Size column; click it to sort.
• Time. Sending 8 MB takes a moment on a phone connection. Local work takes a moment too, but the request list stays quiet.

A tool that processes locally looks different in one specific way: there is no request carrying your bytes. You will still see the page, the fonts, a script or two, maybe an analytics ping. What you will not see is your file going out and coming back.

Two things this test cannot tell you

First, some tools upload in pieces, or over a connection that shows up under a different name. If the request list is confusing, sort by size and look for the biggest thing on it — it is almost always the file.

Second, "we delete your file after one hour" is a promise about their disk, not an absence of the file. Between upload and deletion the file exists on someone else's machine, in a folder with a name they chose, under a retention policy you cannot audit, and sometimes in a backup that outlives the policy. That may be a fine trade. It is not the same thing as never sending it.

Test with a decoy

Never run this experiment with a passport scan or a medical letter. Make a one-page PDF with the word TEST on it, or resize a photo of a plant. You are testing the architecture, not the site's honesty, and a decoy file tells you everything you need to know.

Why this site passes its own test

Every tool here runs in the tab: the file is read by the browser, processed in memory, and handed back to you as a download. Nothing is uploaded, which is why there is no account, no file list, and no "your files are deleted after N hours" promise to make. Open the Network tab on the PDF merger and check. If you find an upload, that is a bug worth reporting.