Your file never uploads
When you drop a PDF, the page reads it with the browser's local file API and keeps it in memory. Compression uses only that memory copy, and the download is generated from the same copy. No request carries your document anywhere - open the developer tools network tab and you will see the file appear in no request at all.
No accounts, no profiles
There is no sign-up, no login and no user database. The tool cannot associate a file with a person because it never meets either.
No tracking at this stage
The site sets no analytics cookies and loads no third-party trackers. All JavaScript - the PDF engine, the packer for zip downloads - is served from this same domain, so nothing phones home.
What remains on your side
Files you download land in your normal downloads folder under your browser's rules. Clearing the tab clears everything the page was holding; there is nothing else to delete on our side, because there is no our side.