A scan of ten pages shouldn't be 20 MB. Open a PDF, keep Balanced, and I save its large images again at a sensible resolution — the text stays selectable, and links, form fields and bookmarks stay exactly as they are. Scans, photo-heavy documents and slide decks exported from design tools gain the most. There are three levels: High quality, Balanced and Smallest file. You see the real saving before you download, and if the PDF is already well compressed I tell you instead of handing you a copy that's barely different. The file is not uploaded; it never leaves your device.