PNG or JPG? The answer depends on the page
JPEG compresses by discarding detail the eye is unlikely to notice, which works brilliantly for photographs and badly for everything that has sharp edges. Text, line drawings, charts and screenshots are full of sharp edges, and JPEG expresses them as smudges and halos — the familiar “ringing” around letters.
PNG compresses losslessly. Every pixel that comes out of the renderer is stored exactly. For a page of text this produces a smaller file than you might expect, because flat white areas compress extremely well. For a page containing a large photograph, PNG can end up five or ten times larger than the equivalent JPEG, and the visible benefit is slight.
The practical rule: PNG for documents, diagrams, charts, screenshots, slides and anything with transparency. JPG for photographs and when file size is the priority. Both tools are free here, so it costs nothing to try one and switch.
When transparency is useful
By default, PDF pages are rendered on a white background — which is what a page actually is. Turning the white background off produces a PNG with an alpha channel, where empty areas of the page are genuinely transparent.
That matters when you are placing a page image on top of something. Dropping a page onto a coloured slide looks wrong with a white rectangle around it and right with transparency. Layering a diagram over a coloured section of a document works the same way.
Note that transparency only applies to empty space, not to white graphics. If a page has a white box drawn on it, that box stays white because it is real content. Transparency reveals what is behind the page, and there is nothing behind a page in a PDF.
Resolution guidance for real tasks
Presentation slides: 150 DPI. A full A4 page at 150 DPI is 1240 pixels wide, which fills a 16:9 slide comfortably even after scaling.
Website and app assets: 150 DPI for standard screens, or 300 DPI if the same asset will also be used on high-density displays where 2× pixel ratios matter.
Printing at A4: 300 DPI. Anything less looks noticeably soft on paper, particularly for small text.
Enlarging a diagram: go higher than 300 DPI if the source page is vector-based, because the text will genuinely be sharper rather than interpolated. There is a guard that stops the canvas exceeding browser limits, so very large requests are scaled down safely rather than failing.
Thumbnails and previews: 72 DPI, first page only. Fast, tiny, and plenty for a list view.
Working with the exported files
Every PNG is named after the source document with its page number, zero-padded so that page 2 sorts before page 10. When you convert several pages, use the ZIP download rather than triggering a dozen separate downloads — browsers will ask permission for each one otherwise.
If the images will be used in a document of their own, import them with the Images to PDF tool to get them back onto properly sized pages. If they need a different size, any image editor can resize a PNG without the cumulative quality loss that repeated JPEG re-encoding causes.
One thing worth knowing: PNG is an excellent archive format precisely because it is lossless. Converting a PDF page to PNG and back to PDF costs nothing in quality, whereas a JPEG round trip loses a little every time. If you plan to edit and re-export repeatedly, keep the PNGs as your master copies.
Storage is worth a thought if you export a lot. A folder of 300 DPI PNGs from a long document can be large enough to fill a phone in a single session, so convert only the pages you need and move the export off the device if you want to keep it. For anything that will be re-edited, keep the PDF as the master and the PNGs as working files — the PDF stays the smaller and more faithful record of the original page.