PNG to PDF Converter

This PNG to PDF converter puts one or many PNG images into a single PDF, one image per page, without losing a pixel. It suits the files PNG is used for — screenshots, diagrams, charts, scanned line art, logos — when they need to travel as one document: a bug report, a set of slides exported as images, a design proof.

PNG is a lossless format, and it stays lossless here. The PDF is built in your browser with the open-source pdf-lib library, which decodes each PNG to its pixels and stores them in the PDF with lossless Deflate compression — the image in the PDF has exactly the pixel values of the PNG. JPG files can be added too; they are copied into the PDF unchanged.

Transparency works the way you would expect on paper. The PNG's alpha channel is stored as a soft mask, so transparent and semi-transparent areas let the page underneath show through — and a PDF page is white. A logo on a transparent background therefore appears on white, with its soft edges intact rather than a hard outline or a black box.

The PDF can come out larger or smaller than the PNG files, because the pixels are compressed again rather than copied. It grows when the PNGs were tightly optimised: pdf-lib stores every PNG as full 8-bit RGB, so palette PNGs (graphics saved with few colours) and greyscale PNGs are expanded to three colour channels, and its Deflate compression skips the per-row filters PNG uses to shrink photographic images. It can shrink when the PNGs were saved with light compression, as many screenshot tools and browsers do. A 16-bit PNG is stored at 8 bits per channel. If size matters more than exactness, convert photographs to JPG first — JPG files go into a PDF without growing.

Page size "Fit to image" makes each page exactly the size of its picture at 96 pixels per inch — 1920 × 1080 px becomes 1440 × 810 pt (20 × 11.25 in) — so nothing is resized. Very large images are scaled down so no page exceeds 200 in (14,400 pt) on a side, the largest page size PDF viewers accept. A4 and US Letter give uniform, printable pages: each image is scaled down to fit inside the margin (none, 0.25 in or 0.5 in) and centred, never enlarged. "Auto" orientation turns the page landscape for wide images.

No upload is involved at any point. The files are read into your browser's memory, the PDF is assembled there and handed back as a download; you can confirm in your browser's developer tools under Network that no request carries your images. Up to 200 images of up to 50 MB each fit in one PDF.

1. Each file's leading bytes are checked for the PNG or JPG signature, so a renamed file of another type is caught and named. 2. Each PNG is decoded to 8-bit RGBA pixels. The RGB values are stored as a Deflate-compressed image; if any pixel is not fully opaque, the alpha values are stored as a soft mask (SMask) so the white page shows through. 3. JPG files are copied into the PDF unchanged. An animated PNG is drawn on a canvas and its first frame is stored. 4. Page size: Fit to image = image pixels × 0.75 pt (96 DPI) plus the margin, scaled down if a side would pass 14,400 pt (200 in); A4 is 595.28 × 841.89 pt and Letter 612 × 792 pt, swapped to landscape when Auto and the image is wider than tall. The image is scaled by min(available width ÷ image width, available height ÷ image height, 1) and centred. 5. Pages follow the list order; one file is saved under its own name with .pdf, several as images.pdf.