Optimize tools

Compress targets the usual culprit: embedded images saved at far higher resolution than the page needs. It re-encodes them at a sensible size, which is why a scan-heavy file can drop by most of its weight while a text-only file barely moves. This part is lossy, so keep the original if the PDF is destined for print.

Repair is for a file that will not open at all. PDFs carry an index of where every object lives, and if that index is truncated or corrupted — an interrupted download, a crashed export — most readers give up even though the page data is still intact. Repair rebuilds the index from what it can find. It recovers most damaged files, though it cannot invent bytes that were never written.