PNG is lossless compression with a full 8-bit alpha channel. PDF is a frozen page layout with no heading structure a machine can rely on. ImageMagick sits between the two, and this page says exactly what happens to a PNG file on the way to becoming a PDF one.
What runs when a PNG file becomes PDF
ImageMagick 6.9.12, on a machine we rent and watch. Your PNG file is uploaded once, ImageMagick runs once, the PDF comes back, and neither file is kept. PNG to PDF is one of the 3649 pairs that engine was probed on with a real file, which is why it has a page here and why the pairs the probe could not prove do not.
What survives from the PNG into the PDF
The pixel dimensions of your PNG file. The PDF comes out the size the PNG went in, because nothing on this path resizes anything.
Every pixel value. PNG and PDF are both lossless, so the PDF file adds no compression artefacts that the PNG did not already have.
What PNG to PDF costs you
Transparency. PDF has no alpha channel, so the engine composites your PNG image onto white before encoding. Without that step ImageMagick lays black underneath, and a transparent PNG logo comes back as a black rectangle.
The chance of getting text out. The PDF you receive is one page with your PNG picture painted on it. Words inside the PNG stay pixels, and nothing reading that PDF will find them.
If a model is going to read the PDF
Worth knowing before the PDF goes anywhere near an assistant: this is the wrong direction for that. A PDF is a set of positioned glyphs, and a model has to reconstruct the reading order before it can begin. If a machine rather than a person is going to read this PNG file, convert it to Markdown instead and skip the reconstruction entirely.
PNG to PDF, measured rather than promised
Running PNG to PDF against the real engine with a real file, ImageMagick wrote 2,536 bytes of PDF in under a tenth of a second, machine otherwise idle. That is one PNG file on one day and not an average, which is why the number is given together with the file that produced it.
The PNG to PDF verdict was reached by a format signature, meaning at least four bytes unique to the format were found at the right offset. Which check was used matters, because they do not all prove the same thing, and a status code of 200 proves nothing whatsoever about whether the PDF file has anything inside it.
The same PNG file, sent somewhere else
Other outputs the probe measured out of a PNG file, so the cost of choosing PDF can be read against something. Sizes do not compare across engines, because each family was probed with its own PNG witness file.
PNG to JPG: 1,568 bytes in under a tenth of a second, verified by a format signature.
PNG to WEBP: 370 bytes in under a tenth of a second, verified by a format signature.
PNG to GIF: 3,512 bytes in 0.1 seconds, verified by a format signature.
PNG to TIFF: 1,466 bytes in under a tenth of a second, verified by a format signature.
Other ways into PDF, and what they measured
Among the published routes into PDF, PNG is the number 26 largest output of the 26 measured. The witness files differ, so this ranks the probe run and not your document.
WEBP to PDF: 94,782 bytes in under a tenth of a second.
TIFF to PDF: 118,721 bytes in under a tenth of a second.
SVG to PDF: 4,195 bytes in under a tenth of a second.
HEIC to PDF: 94,782 bytes in under a tenth of a second.
BMP to PDF: 118,745 bytes in under a tenth of a second.
What we will not pretend about PNG to PDF
A PNG file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A PNG to PDF run that passes 30 seconds is killed, and the ImageMagick process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
No text is read out of the PNG anywhere on this path. Converting a picture to PDF never turns it into words, whatever the picture happens to contain.
ImageMagick was not saturated at sixteen simultaneous conversions: it held 47.5 a second while latency moved from 0.22 s to 0.34 s, and the service memory did not move off 51 MB. That is the measured headroom behind PNG to PDF, not a marketing number.
One PNG file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
PNG to PDF: what people ask
What actually converts my PNG file to PDF?
ImageMagick does it, 6.9.12, on a machine we rent and watch. Not a browser trick and not somebody else service: the PNG file is uploaded once, ImageMagick runs once, the PDF comes back, and neither file is kept afterwards.
How long does PNG to PDF take?
On the file the probe used, ImageMagick took under a tenth of a second and wrote 2,536 bytes of PDF. That is one real measurement on one real PNG file, not an average and not a promise about yours: a larger PNG takes longer, and past 30 seconds the run is stopped.
What do I lose going from PNG to PDF?
The one to know about first: Transparency. PDF has no alpha channel, so the engine composites your PNG image onto white before encoding. Without that step ImageMagick lays black underneath, and a transparent PNG logo comes back as a black rectangle.
Can I put several PNG files into one PDF?
No. One PNG file goes in and one PDF comes out, with that picture on it. Nothing here merges files, orders them or numbers pages: it is one upload, one conversion, one download, and that is the whole of what this page does.
Is PNG to PDF free?
There is a free allowance every month, and one PNG to PDF conversion costs half a credit against it. When the allowance runs out the tool says so and stops, rather than quietly handing you a worse PDF.