Best for scans and photo-heavy PDFs. Text will no longer be selectable in the result. Everything runs in your browser — nothing is uploaded.
This works by turning each page into an image and recompressing it — the same trick that shrinks most large PDFs, which are usually scans or photos rather than plain text. The tradeoff: text in the output is no longer selectable or searchable. If you need the text to stay selectable, use Extract PDF Text instead of compressing, or don't compress a text-based PDF at all.