Why PNG pages should not become JPEG
PNG is what screens produce: screenshots, exported charts, scanned forms saved by an app, a receipt captured from a banking page. Their content is hard edges and flat areas, which is exactly what JPEG handles worst. Run a screenshot of small print through JPEG and every letter grows a faint grey halo; run a chart through it and the flat colour shimmers. Most converters do this anyway, because JPEG is the easy way to put a picture in a PDF.
This page writes pages from PNG files losslessly instead. The pixels are filtered row by row with the same “Up” predictor PNG uses and compressed with Flate, so a row that repeats the one above it costs almost nothing, and the reader rebuilds the exact samples on screen. No resolution ceiling is set when the page opens, so the pixels are not resampled either; a 1080-pixel-wide screenshot is 1080 pixels wide in the PDF.
A worked example from our test set: a 1080 × 2340 phone screenshot of a chat, with lossless pages on, made a one-page PDF of 185 KB whose image decodes to exactly the PNG’s pixels — every sample compared, none different. The same screenshot written as JPEG at the usual quality came to 217 KB, so for a page of flat colour and type, lossless was both sharper and smaller. A transparent logo in the same run landed on plain white paper.
Transparency, paper and size
A PDF page is paper, so anything see-through in a PNG has to land on something. Here it lands on the paper colour: white by default, or ivory, stone, charcoal or any colour you pick on the Pages step. The notice beside the Lossless option says so, because a logo that was designed for a dark background will look different on white.
Lossless pages cost space. If the upload box has a limit, the builder will still measure and meet a target — by redrawing the JPEG pages in the document — but it never quietly turns a lossless page into JPEG to get there; it tells you how close it came and leaves that choice to you. For a strict limit, the size-limited builder or the 200 KB route start with the levers set. Photos from a phone are better served by JPG to PDF, which copies them without any recompression at all.
Questions about PNG to PDF
Is the PNG really kept lossless?
Yes, with Lossless pages on, which is how this page opens. Each page from a PNG is written as Flate-compressed samples — the same family of compression PNG itself uses — so every pixel in the PDF is the pixel that was painted from your file. Nothing is turned into JPEG unless you switch the option off.
Are my photos uploaded?
No. The PNGs are decoded by your browser, painted onto pages and compressed in this tab. The finished PDF is handed to your Downloads folder; no request carrying a picture is made.
What does the PDF contain?
One lossless image per page and nothing else: no text layer, no metadata from the PNG, and no title, author or producer field. Text in a screenshot is part of the picture, so it cannot be selected or searched.
What happens to a transparent background?
Transparent areas are filled with the paper colour, which is white unless you pick another on the Pages step. A logo with a cut-out edge therefore sits on the page the way it would on paper, rather than on a black or checkered box.
Why is the lossless file bigger than a JPEG one?
Because it keeps every pixel. A screenshot full of flat colour stays small, but a PNG of a photograph can be several times larger than the same page in JPEG. If the size matters more than the last bit of sharpness, turn Lossless pages off on the Quality step and set a size; the solver never makes that trade for you.