PDF is a frozen page layout with no heading structure a machine can rely on. HEIC is what an iPhone writes unless you tell it not to: HEVC compression inside an ISO container, about half the size of the JPEG it replaced. ImageMagick sits between the two, and this page says exactly what happens to a PDF file on the way to becoming a HEIC one.
What runs when a PDF file becomes HEIC
ImageMagick 6.9.12, on a machine we rent and watch. Your PDF file is uploaded once, ImageMagick runs once, the HEIC comes back, and neither file is kept. PDF to HEIC 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 PDF into the HEIC
The pixel dimensions of your PDF file. The HEIC comes out the size the PDF went in, because nothing on this path resizes anything.
What PDF to HEIC costs you
Scalability. PDF describes shapes, HEIC stores a grid of pixels, and the engine rasterises at 150 dots per inch on the way across. That density is a deliberate choice: at the 72 dpi ImageMagick defaults to, an A4 PDF page comes out 595 pixels wide and reads as a failed conversion. Enlarge the HEIC afterwards and it blurs, because there is nothing left to redraw from.
Every page of the PDF but the first. A PDF file can hold several images in one container; a HEIC file holds exactly one.
Exactness. HEIC is a lossy encoding, so the file you get back approximates the PDF you sent. The artefacts appear once and never come out again, which is why converting the HEIC back to PDF afterwards restores nothing.
The PDF text layer. A PDF usually carries selectable text; this path treats the page as a picture and paints it, so what comes out is an image of the page rather than its words.
If a model is going to read the HEIC
A HEIC file is pixels, and pixels are expensive for a model to read. Handed this HEIC, an assistant spends its budget looking at the picture rather than reading it, and it will paraphrase what it thinks it saw. If your PDF is mostly words, the useful move is to pull the text out of it, not to change which picture format holds it.
PDF to HEIC, measured rather than promised
Running PDF to HEIC against the real engine with a real file, ImageMagick wrote 982 bytes of HEIC in 0.1 seconds, machine otherwise idle. That is one PDF file on one day and not an average, which is why the number is given together with the file that produced it.
The PDF to HEIC 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 HEIC file has anything inside it.
The same PDF file, sent somewhere else
Other outputs the probe measured out of a PDF file, so the cost of choosing HEIC can be read against something. Sizes do not compare across engines, because each family was probed with its own PDF witness file.
PDF to DOCX: 23,905 bytes in 0.9 seconds, verified by a format signature.
PDF to EPUB: 26,909 bytes in 0.9 seconds, verified by a format signature.
PDF to JPG: 5,782 bytes in 0.1 seconds, verified by a format signature.
PDF to PNG: 1,294 bytes in 0.1 seconds, verified by a format signature.
PDF to WEBP: 906 bytes in 0.1 seconds, verified by a format signature.
PDF to TXT: 219 bytes in 0.8 seconds, verified by reading the text back.
Other ways into HEIC, and what they measured
Among the published routes into HEIC, PDF is the third largest output of the 10 measured. The witness files differ, so this ranks the probe run and not your document.
JPG to HEIC: 505 bytes in under a tenth of a second.
BMP to HEIC: 500 bytes in under a tenth of a second.
GIF to HEIC: 5,402 bytes in 0.1 seconds.
HEIF to HEIC: 486 bytes in under a tenth of a second.
ICO to HEIC: 807 bytes in 0.1 seconds.
What we will not pretend about PDF to HEIC
A PDF file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A PDF to HEIC 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.
Until the end of August this machine could not read a HEIC at all, and reported the opposite. ImageMagick declared HEIC readable, but libheif carried only its AV1 plugins, which serve AVIF; the HEVC decoder was absent, and a HEIC decoded quietly as something else. The plugin was installed on the 30th, and that is the whole reason this pair exists.
The PDF to HEIC proof used a file genuinely encoded in HEVC, and that detail is not pedantry: ImageMagick refuses to write HEIC and hands you a PNG under that name if you ask it to, so a HEIC forged for the test would have made a false result look like a true one. The HEIC it produced was 982 bytes, recognised by a format signature.
No text is read out of the PDF anywhere on this path. Converting a picture to HEIC 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 PDF to HEIC, not a marketing number.
One PDF file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
PDF to HEIC: what people ask
What actually converts my PDF file to HEIC?
ImageMagick does it, 6.9.12, on a machine we rent and watch. Not a browser trick and not somebody else service: the PDF file is uploaded once, ImageMagick runs once, the HEIC comes back, and neither file is kept afterwards.
How long does PDF to HEIC take?
On the file the probe used, ImageMagick took 0.1 seconds and wrote 982 bytes of HEIC. That is one real measurement on one real PDF file, not an average and not a promise about yours: a larger PDF takes longer, and past 30 seconds the run is stopped.
What do I lose going from PDF to HEIC?
The one to know about first: Scalability. PDF describes shapes, HEIC stores a grid of pixels, and the engine rasterises at 150 dots per inch on the way across. That density is a deliberate choice: at the 72 dpi ImageMagick defaults to, an A4 PDF page comes out 595 pixels wide and reads as a failed conversion. Enlarge the HEIC afterwards and it blurs, because there is nothing left to redraw from.
My PDF has several pages. Which one becomes the HEIC?
The first, and only the first, because a HEIC file holds one image. That page is rasterised at 150 dots per inch, and the words on it arrive as pixels: this path paints the page rather than reading it.
Is PDF to HEIC free?
There is a free allowance every month, and one PDF to HEIC 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 HEIC.