no compression, no upload
PNG keeps every pixel exactly as it was drawn
JPG is built for photographs: it throws away detail you are unlikely to notice, which is precisely the wrong trade for a page of text. Around small type and thin lines that shows up as grey fuzz, and every re-save makes it worse.
PNG stores the page losslessly, so a screenshot of a diagram stays as crisp as the diagram. This page renders those images in your browser using the PDF engine it already has, which also means your document never goes anywhere.
three steps
How to convert PDF to PNG
Add the file
Drop in a PDF — the first page appears as a preview.
Pick pages and size
Every page or a range, at 1×, 2× or 3× resolution.
Download
One PNG, or a ZIP when you export several pages.