Strong rasterizes each page to an image and rebuilds the PDF — the biggest shrink, especially on scans, but the text becomes an image (no longer selectable or searchable). Light is a lossless re-save that keeps the text and everything else; the reduction is more modest but nothing is lost.

Right in your browser. It's a web app that compresses locally rather than sending your documents off to a server, so there's no queue and nothing to cap.

Yes — that's the trade for the size. Strong turns each page into an image, so the file looks the same but the text can't be selected, searched or copied. Use Light if you need the text to stay real.

As many as your device can hold in memory — there's no per-batch limit. They compress one after another and download together as a single zip.

Light is lossless, so a PDF that's already efficiently saved may barely shrink. When that happens you get your original back rather than a larger file — try Strong if you need a real size cut and don't need selectable text.