JPEG is lossy compression tuned for human vision, and no alpha channel at all. 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 JPG file on the way to becoming a PDF one.
What runs when a JPG file becomes PDF
ImageMagick 6.9.12, on a machine we rent and watch. Your JPG file is uploaded once, ImageMagick runs once, the PDF comes back, and neither file is kept. JPG 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 JPG into the PDF
The pixel dimensions of your JPG file. The PDF comes out the size the JPG went in, because nothing on this path resizes anything.
What JPG to PDF costs you
The chance of getting text out. The PDF you receive is one page with your JPG picture painted on it. Words inside the JPG stay pixels, and nothing reading that PDF will find them.
Nothing further, and that is the point worth making: PDF cannot undo what JPG already threw away. The compression artefacts are baked into the pixels, PDF stores them faithfully, and the file usually comes out several times larger for exactly the same picture.
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 JPG file, convert it to Markdown instead and skip the reconstruction entirely.
JPG to PDF, measured rather than promised
Running JPG to PDF against the real engine with a real file, ImageMagick wrote 4,232 bytes of PDF in under a tenth of a second, machine otherwise idle. That is one JPG file on one day and not an average, which is why the number is given together with the file that produced it.
The JPG 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 JPG file, sent somewhere else
Other outputs the probe measured out of a JPG 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 JPG witness file.
JPG to PNG: 805 bytes in under a tenth of a second, verified by a format signature.
JPG to WEBP: 350 bytes in under a tenth of a second, verified by a format signature.
JPG to GIF: 3,487 bytes in 0.1 seconds, verified by a format signature.
JPG to TIFF: 72,264 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, JPG is the number 24 largest output of the 26 measured. The witness files differ, so this ranks the probe run and not your document.
PNG to PDF: 2,536 bytes in under a tenth of a second.
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.
What we will not pretend about JPG to PDF
A JPG file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A JPG 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 JPG 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 JPG to PDF, not a marketing number.
One JPG file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
JPG to PDF: what people ask
What actually converts my JPG 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 JPG file is uploaded once, ImageMagick runs once, the PDF comes back, and neither file is kept afterwards.
How long does JPG to PDF take?
On the file the probe used, ImageMagick took under a tenth of a second and wrote 4,232 bytes of PDF. That is one real measurement on one real JPG file, not an average and not a promise about yours: a larger JPG takes longer, and past 30 seconds the run is stopped.
What do I lose going from JPG to PDF?
The one to know about first: The chance of getting text out. The PDF you receive is one page with your JPG picture painted on it. Words inside the JPG stay pixels, and nothing reading that PDF will find them.
Can I put several JPG files into one PDF?
No. One JPG 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 JPG to PDF free?
There is a free allowance every month, and one JPG 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.