PNG to PDF

PNG to PDF writes a new document holding one page per image, and pdf-lib does the embedding. What lands on the page is not the PNG file itself: the library decodes it to raw pixels, stores the colour channels as a Flate-compressed image and splits the alpha channel off into a separate soft mask. No lossy codec is anywhere in that path, so an ordinary eight-bit PNG arrives on the page with the same pixel values it had on disk — none of the softening around sharp edges that makes a lossy encoder the wrong choice for screenshots and line art. What does not survive is the file's own encoding, which is rebuilt rather than carried across.

Transparency survives the trip, which is the part that separates this from converting a photograph. The alpha channel becomes a soft mask on the image, and whatever is transparent shows the Page background colour painted underneath it — white unless you move the swatch. Set that colour deliberately when your images have knocked-out corners or a soft shadow, because it becomes the visible background of the finished page rather than a neutral nothing.

The Page size menu decides the geometry, and its default deserves a warning. Fit the page to each image treats one pixel as one PDF point — a seventy-second of an inch — so the sheet comes out the size of the picture, with any margin added around it rather than eaten out of it. That reads well on screen and holds the image at native resolution, but a 2560-pixel-wide screenshot becomes a page around 900 mm across, which no printer will take without shrinking it first. Choose A4, US Letter, A3 or A5 when the file is going to paper: each image is then scaled to the largest size that fits inside the sheet, proportions kept, centred, with the margin you set in millimetres taken off every edge beforehand.

Two limits are worth knowing before you start. What comes out is a picture of a page, not a document: text inside a screenshot stays a bitmap, so the result cannot be searched or copied from, and PDF OCR is the tool that changes that. And the finished file is normally heavier than the images that went into it, because PNG's per-row filters and its colour palette are discarded and every page stores plain eight-bit RGB samples instead — a compact indexed graphic can come out around three times its original size. Run Compress PDF afterwards if the document has to travel by email. All of it happens in this browser tab through pdf-lib, which this site serves itself: the images are read from disk into memory and the document is handed straight back, with no copy going anywhere.

One format note before you queue a folder up. A 16-bit-per-channel PNG is reduced to 8 bits per channel on the way in, and an embedded colour profile is dropped because each page is written as DeviceRGB, so a wide-gamut export can shift slightly. Animated PNGs are refused outright rather than flattened to their first frame.

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