Short answer
To convert a PDF to PNG, choose your file and switch the output to PNG — each page is rendered to a lossless PNG image in your browser, with nothing uploaded. Download pages one by one or all at once.
PNG is lossless, so it's the better choice when you need crisp text or line art with no JPG compression artifacts — at the cost of larger files. For photos, JPG is usually smaller with no visible difference.
Every page is rendered on your device, so a confidential PDF never leaves it.
PNG for crisp text/line art (lossless, larger); JPG for photos (smaller). Both are offered here.
No — pages are rendered to images in your browser.