There are three sensible ways to turn a PDF page into an image, and the only real decision is the format: JPG, PNG, or WebP. They render the same pixels at the same resolution — the difference is entirely in how those pixels are stored, which decides the file size, whether the image is pixel-perfect, and whether older software can open it.
This guide explains what each format is good at, shows measured file sizes on the same document, and helps you pick without trial and error.
The short answer
Choose JPG when you want a small, universally compatible image and the page is mostly photos or scans — JPG is lossy, so it trades a little fidelity for size, and every piece of software on earth opens it. Choose PNG when you want the image to be pixel-perfect — it is lossless, so text edges and thin lines stay crisp with no compression artefacts, at the cost of a larger file. Choose WebP when you want the smallest file and your software is current — it holds JPG-level quality in a smaller file than either, and every modern browser and most current apps read it.
Measured on the same document
Numbers make the trade-off concrete. We rendered the same five-page A4 PDF to each format at 300 DPI — identical 2481-pixel-wide pages in every case — and measured the download:
PNG came out at about 679 KB, JPG at about 247 KB, and WebP at about 92 KB. So on this document WebP was roughly a third the size of JPG and a seventh the size of PNG, for the same resolution. The exact sizes depend on what is on the page — a photo-heavy page compresses very differently from a page of text — but the ordering is typical: WebP smallest, JPG in the middle, PNG largest because it throws nothing away.
The resolution is identical across all three. The format changes the bytes, not the pixel dimensions, so none of these choices makes the image larger or smaller on screen — only on disk.
When each one is the right call
Use PNG for anything where sharpness matters more than size: a page of text or a diagram you will zoom into, a screenshot you will mark up, or any image you will edit further (each lossy re-save of a JPG degrades it; PNG does not). Use JPG when you need broad compatibility or the page is a photo or a scan, where lossless storage buys you nothing visible but costs you size. Use WebP when file size is the priority and you control where the image is used — a website, an app, a document you are assembling — and you know the destination can read it.
The one place to avoid WebP is when you must hand the file to unknown or older software: some legacy image viewers and a few older office applications still do not open it. If in doubt, JPG is the safe default.
What 300 DPI versus 150 DPI changes
DPI — dots per inch — is the resolution. At 300 DPI an A4 page comes out about 2480 pixels wide, which is print quality: you can enlarge it, print it, and the text stays sharp. At 150 DPI the same page is about 1240 pixels wide, which is fine for viewing on a screen and produces a smaller file. The number is the true resolution of the image, not a setting that approximates one — you can confirm it by dividing the pixel width by the page width in inches.
Pick 300 DPI when the image might be printed or zoomed, and 150 DPI when it is only for screen and you want it lighter. This choice is independent of the format: any of the three can be produced at either resolution.
Doing it without uploading the file
Most online converters upload your PDF to a server to render it. That is worth avoiding for anything you would not email to a stranger — a contract, an ID, a medical record. It is not necessary: a modern browser can render a PDF page to an image on your own device, with the file never leaving your computer.
Filum's PDF to JPG, PDF to PNG, and PDF to WebP tools all work this way — entirely in the browser, no upload, no account, and they even work offline. Each lets you choose 300 or 150 DPI and shows you the page count and resolution of what it produced, so the quality is something you can verify rather than take on trust. If you are choosing a format, the easiest test is to run the same PDF through two of them and compare the downloads.