If your slides are already a PDF (or you export them to one), you don't need to open PowerPoint, Keynote, or Google Slides just to present them. This tool turns a PDF into a full-screen slideshow you can control with the arrow keys or by clicking, right in your browser, which is handy when presenting from a borrowed computer, a Chromebook, or anywhere you can't rely on having the original software installed.
Not currently. PowerPoint files are a complex format that's genuinely hard to render accurately outside of PowerPoint itself. Export your slides to PDF first (a one-click option in PowerPoint, Keynote, and Google Slides), then present the PDF here.
No, it displays exactly what's on each PDF page. If you need speaker notes visible only to you, that's a separate, more complex presenter-view feature this tool doesn't attempt.
No. The PDF is rendered entirely in your browser using the same engine that powers Firefox and Chrome's built-in PDF viewers. Nothing is sent to a server.