Drop in a PDF and each page is rendered as an image. Pick only the pages you want with a range like '1-3, 5, 8-', choose the resolution (96, 150 or 300 dpi) and the format (JPG or PNG). When you take several pages at once they arrive as a single ZIP, so the browser never has to ask about a dozen separate downloads. Nothing is uploaded — the whole conversion happens in your browser.
Rendering a very large page at high resolution can exceed the browser's canvas limit. When that happens the page is drawn at a lower resolution and the tool says so, rather than silently handing you a blank image.
PNG keeps text, tables and thin lines crisp. If the page is mostly photographic — a scan or an image-heavy layout — JPG is far smaller with no visible difference.
96 dpi for viewing on a screen or posting online, 300 dpi for printing. 150 sits in the middle and is enough for most uses.
No. A scanned PDF already contains an image, so it cannot come out sharper than the original scan. Raising the resolution only makes the file bigger.
No. Reading the PDF and rendering the images both happen in your browser. The only network request is the code for the page itself.