Who runs this
MillFile is built and maintained by one independent developer. There is no company behind it and no team, which is also why there is no sign-up, no pricing table and no account to create.
There is no upload step on this site, so no server of ours ever holds a copy of a file you process.
What it does
Upload forms all over the web enforce a fixed PDF limit: 100 KB for an ID scan, 300 KB for an application, 1 MB for an attachment. When you miss the limit the form returns one line of error text and no hint about what to do next.
MillFile rebuilds your document to fit the number you pick. A lossless rebuild runs first and keeps the text selectable; only if the file is still too large are pages re-rendered with less detail, one step at a time, until they fit. You get the finished file back as an ordinary download.
Why it works this way
Most PDF tools ask you to upload the document to their server first. That is fine for a takeaway menu and a bad idea for a passport scan, a payslip, a medical certificate or a signed contract - which are exactly the documents people need to compress.
Doing the work in the browser removes that step, and with it the queue, the daily cap and the watermark, because there is no server to pay for. The trade is time: a very large document takes longer here, since every page is rendered on your own machine.
When a document cannot reach the target you chose, the badge reports the smallest size actually achieved instead of claiming success. Knowing the real floor is more useful than a reassuring number.
Contact
Questions, bug reports and complaints all go to the same address: hello@millfile.com.
If a PDF does not compress the way you expected, mention the target you chose, roughly how large the original was and whether it was a scan or an exported document. That is usually enough to reproduce it.