What dpi means for your images

A PDF page has a size in inches or centimeters, not in pixels. The resolution, in dots per inch, decides how many pixels each inch of paper becomes. An A4 page is about 8.3 by 11.7 inches, so:

72 dpi gives roughly 600 by 840 pixels. Fine for a thumbnail or a quick look, too soft for reading small print.
150 dpi gives roughly 1240 by 1750 pixels. Text is sharp on laptop and phone screens, and files stay a reasonable size. This is the default.
300 dpi gives roughly 2480 by 3510 pixels, the usual resolution for printing. Files are about four times as large as at 150 dpi, so only pick it when you need the detail.

JPG or PNG

JPG is the safe choice for sharing. It is small, every app opens it, and it handles scanned pages and photos well. Around very sharp edges, such as black text on white, it can leave faint smudges if you look closely.

PNG stores every pixel exactly, so text, lines and charts stay perfectly crisp. The price is size: a page of text can easily be three to five times larger than the same page as JPG. If you need only the PNG version, that page starts with PNG selected.

Your PDF stays on your device

The pages are drawn by PDF.js, the open-source renderer Firefox uses for its own PDF viewer, running inside this page. The images are encoded by your browser and, when there are several, packed into a .zip in memory too. Nothing is uploaded, which matters for bank statements, contracts and anything else you would rather not hand to a website.

To keep part of a PDF as a PDF rather than as images, use Split PDF.
To go the other way and turn photos or scans into one PDF, use JPG to PDF.
Password-protected PDFs cannot be opened here; save an unprotected copy first.

Frequently asked questions

Which resolution should I choose?

150 dpi is right for most things: an A4 page comes out about 1240 by 1750 pixels, sharp on a laptop or phone screen. Choose 300 dpi when the image will be printed or when you need to zoom into small print. 72 dpi gives small, quick previews.

Should I pick JPG or PNG?

JPG makes much smaller files and is accepted almost everywhere, which suits scanned pages and pages with photos. PNG keeps text and thin lines perfectly crisp, at the cost of larger files, so it is the better choice for slides, diagrams and text you want to stay sharp.

Is my PDF uploaded?

No. The pages are drawn by PDF.js, an open-source PDF renderer, inside your browser, and the images are created in the page's memory. Nothing is sent to a server, so payslips, contracts and medical letters stay on your device.

Why was a page saved smaller than the resolution I chose?

Very large pages, such as posters or technical drawings, would need hundreds of megapixels at 300 dpi and could crash the browser tab. Each image is capped at about 16.7 megapixels, which still covers A4 and Letter at 300 dpi. When a page is scaled down, the tool tells you which one.

Can I convert a password-protected PDF?

No. Open the file with its password in your PDF reader, save an unprotected copy, and convert that.