Each page comes out as its own image. Pick JPG for something small enough to email, or PNG when you need it crisp.
The PDF reader loads only when you drop a file in, so the page itself stays light. Your file is read on your own machine and never sent anywhere — open your browser's network tab and watch while you use it.
You choose. 144 DPI is right for the screen, 216 DPI for printing, and 288 DPI when someone is going to zoom in.
Yes — there is a button for all of them, and one per page if you only want a few.
Everything here is free and works the same way — in your browser.