About JPG → PNG
Does JPG-to-PNG add transparency?
No. JPG never had transparency to begin with, so the resulting PNG is fully opaque. If you need to remove a background, you'll need an editor with masking tools — verto's job is faithful format conversion, not editing.
Will the PNG be bigger than the JPG?
Almost always, yes. PNG is lossless; JPG is lossy. The PNG cannot recover the detail JPG threw away, but it has to encode every pixel exactly, so the file ends up significantly larger. Convert to PNG only when you actually need PNG.
Is anything uploaded?
Nothing. verto is a static page. Your JPG is decoded by the browser's Canvas API, re-encoded as PNG locally, and handed back to you as a download. Nothing touches a server.