ICO is a Windows icon, capped at 256 pixels a side by the file structure itself. 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 an ICO file on the way to becoming a PDF one.
What runs when an ICO file becomes PDF
ImageMagick 6.9.12, on a machine we rent and watch. Your ICO file is uploaded once, ImageMagick runs once, the PDF comes back, and neither file is kept. ICO 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 ICO into the PDF
The pixel dimensions of your ICO file. The PDF comes out the size the ICO went in, because nothing on this path resizes anything.
Every pixel value. ICO and PDF are both lossless, so the PDF file adds no compression artefacts that the ICO did not already have.
What ICO to PDF costs you
Transparency. PDF has no alpha channel, so the engine composites your ICO image onto white before encoding. Without that step ImageMagick lays black underneath, and a transparent ICO logo comes back as a black rectangle.
The chance of getting text out. The PDF you receive is one page with your ICO picture painted on it. Words inside the ICO 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 ICO file, convert it to Markdown instead and skip the reconstruction entirely.
ICO to PDF, measured rather than promised
Running ICO to PDF against the real engine with a real file, ImageMagick wrote 95,344 bytes of PDF in under a tenth of a second, machine otherwise idle. That is one ICO file on one day and not an average, which is why the number is given together with the file that produced it.
The ICO 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 ICO file, sent somewhere else
Other outputs the probe measured out of an ICO 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 ICO witness file.
ICO to JPG: 1,568 bytes in under a tenth of a second, verified by a format signature.
ICO to PNG: 810 bytes in under a tenth of a second, verified by a format signature.
ICO to WEBP: 370 bytes in under a tenth of a second, verified by a format signature.
ICO to GIF: 3,799 bytes in 0.1 seconds, verified by a format signature.
ICO to TIFF: 96,278 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, ICO is the fourth largest output of the 26 measured. The witness files differ, so this ranks the probe run and not your document.
DOCX to PDF: 11,917 bytes in 1.2 seconds.
DOC to PDF: 11,917 bytes in 1.1 seconds.
XLSX to PDF: 18,965 bytes in 1.1 seconds.
XLS to PDF: 18,519 bytes in 1.0 seconds.
PPTX to PDF: 20,929 bytes in 1.2 seconds.
What we will not pretend about ICO to PDF
An ICO file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
An ICO 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 ICO 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 ICO to PDF, not a marketing number.
One ICO file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
ICO to PDF: what people ask
What actually converts my ICO 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 ICO file is uploaded once, ImageMagick runs once, the PDF comes back, and neither file is kept afterwards.
How long does ICO to PDF take?
On the file the probe used, ImageMagick took under a tenth of a second and wrote 95,344 bytes of PDF. That is one real measurement on one real ICO file, not an average and not a promise about yours: a larger ICO takes longer, and past 30 seconds the run is stopped.
What do I lose going from ICO to PDF?
The one to know about first: Transparency. PDF has no alpha channel, so the engine composites your ICO image onto white before encoding. Without that step ImageMagick lays black underneath, and a transparent ICO logo comes back as a black rectangle.
Can I put several ICO files into one PDF?
No. One ICO 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 ICO to PDF free?
There is a free allowance every month, and one ICO 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.