DOCX is Word in the OOXML format, with headings, tables and named styles. JSON is a data tree of objects, lists, numbers and strings. pandoc sits between the two, and this page says exactly what happens to a DOCX file on the way to becoming a JSON one.
What runs when a DOCX file becomes JSON
pandoc in two passes, on a machine we rent and watch. Your DOCX file is uploaded once, pandoc runs once, the JSON comes back, and neither file is kept. DOCX to JSON 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 DOCX into the JSON
Lists from the DOCX file, nesting included, plus code blocks, block quotes and links, all re-expressed in JSON.
Images: pandoc extracts them out of the DOCX file into a working directory and re-embeds them in the JSON, so nothing ends up pointing at a file that no longer exists.
What DOCX to JSON costs you
Page layout. DOCX carries some and JSON carries none, so margins, page breaks, headers and footers have nowhere to land and are simply not written.
Tables. The JSON writer cannot carry one, and the probe caught this the hard way: a CSV file, which is nothing but a table, came back as a well formed and completely empty JSON with a zero return code. The engine now refuses that case outright rather than handing you the emptiness.
Where DOCX and JSON files come from
DOCX. Word writes it, and so does Google Docs on export. It is ISO/IEC 29500, a zip of XML, which is what lets a program read the document without opening Word.
If a model is going to read the JSON
Structure is what survives from the DOCX file, and structure is what a model needs. DOCX in, JSON out, with the heading tree intact instead of flattened into one long paragraph.
DOCX to JSON, measured rather than promised
Running DOCX to JSON against the real engine with a real file, pandoc wrote 1,722 bytes of JSON in 0.1 seconds, machine otherwise idle. That is one DOCX file on one day and not an average, which is why the number is given together with the file that produced it.
The DOCX to JSON verdict was reached by a pandoc round trip, meaning the output was read back by pandoc and had to still contain a witness word planted in the source, which proves the content travelled and not merely the container. 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 JSON file has anything inside it.
The same DOCX file, sent somewhere else
Other outputs the probe measured out of a DOCX file, so the cost of choosing JSON can be read against something. Sizes do not compare across engines, because each family was probed with its own DOCX witness file.
DOCX to PDF: 11,917 bytes in 1.2 seconds, verified by a format signature.
DOCX to MD: 266 bytes in 0.1 seconds, verified by a pandoc round trip.
DOCX to EPUB: 5,040 bytes in 0.1 seconds, verified by a pandoc round trip.
DOCX to TXT: 264 bytes in 0.1 seconds, verified by reading the text back.
DOCX to HTML: 4,018 bytes in 0.1 seconds, verified by a pandoc round trip.
DOCX to RTF: 4,205 bytes in 1.1 seconds, verified by reading the internal type and finding a witness word.
Other ways into JSON, and what they measured
Among the published routes into JSON, DOCX is the fifth largest output of the 8 measured. The witness files differ, so this ranks the probe run and not your document.
HTML to JSON: 2,058 bytes in under a tenth of a second.
MD to JSON: 1,726 bytes in under a tenth of a second.
ODT to JSON: 1,761 bytes in 0.1 seconds.
RTF to JSON: 1,743 bytes in 0.1 seconds.
TXT to JSON: 1,343 bytes in under a tenth of a second.
What we will not pretend about DOCX to JSON
A DOCX file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A DOCX to JSON run that passes 60 seconds is killed, and the pandoc process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
32 of the 935 pairs probed in the family that serves DOCX to JSON failed, and this pair is not one of them. They fail for reasons worth knowing: a writer that cannot carry what the document is made of, or output the engine could not read back. They are counted here rather than hidden, because a pair that fails quietly is worse than one that fails loudly.
pandoc never writes the JSON through a TeX engine here, and it never writes PDF at all: the eleven engines it would need are not on this machine and a TeX distribution weighs several gigabytes. Anyone who wants a PDF out of a DOCX file goes through LibreOffice or calibre, both of which genuinely can.
One DOCX file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
DOCX to JSON: what people ask
What actually converts my DOCX file to JSON?
pandoc does it, in two passes, on a machine we rent and watch. Not a browser trick and not somebody else service: the DOCX file is uploaded once, pandoc runs once, the JSON comes back, and neither file is kept afterwards.
How long does DOCX to JSON take?
On the file the probe used, pandoc took 0.1 seconds and wrote 1,722 bytes of JSON. That is one real measurement on one real DOCX file, not an average and not a promise about yours: a larger DOCX takes longer, and past 60 seconds the run is stopped.
What do I lose going from DOCX to JSON?
The one to know about first: Page layout. DOCX carries some and JSON carries none, so margins, page breaks, headers and footers have nowhere to land and are simply not written.
Are the tables in my DOCX file still tables in the JSON?
No, and that is a property of JSON rather than a defect of this path. JSON cannot hold a table, so a DOCX file built around one is the wrong candidate for this pair.
Is DOCX to JSON free?
There is a free allowance every month, and one DOCX to JSON 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 JSON.