CSV is one table and nothing else, with no formulas and no cell formatting. DOCX is Word in the OOXML format, with headings, tables and named styles. pandoc sits between the two, and this page says exactly what happens to a CSV file on the way to becoming a DOCX one.
What runs when a CSV file becomes DOCX
pandoc in two passes, on a machine we rent and watch. Your CSV file is uploaded once, pandoc runs once, the DOCX comes back, and neither file is kept. CSV to DOCX 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 CSV into the DOCX
Tables, rebuilt in DOCX syntax rather than screenshotted. That is the difference between a table a machine can read and a picture of one, and it is the whole reason to send a CSV file through pandoc rather than through a printer.
Lists from the CSV file, nesting included, plus code blocks, block quotes and links, all re-expressed in DOCX.
Images: pandoc extracts them out of the CSV file into a working directory and re-embeds them in the DOCX, so nothing ends up pointing at a file that no longer exists.
What CSV to DOCX costs you
Nothing that was ever there, which is the honest answer for this pair: a CSV file has no page layout to lose. The DOCX you get uses the default Word template, so it is a plain document rather than a designed one.
Where CSV and DOCX files come from
CSV. Everything writes it and nothing agrees on it. There is an RFC, 4180, and it describes common practice rather than commanding it: quoting, escaping and line endings all vary by producer. A CSV is the lowest common denominator, which is both why it is everywhere and why it surprises people.
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 DOCX
DOCX is a good destination for a person and a mediocre one for a model: the structure is real but buried in XML with a great deal of packaging around it. If the next reader of this CSV file is an assistant rather than a colleague, CSV to Markdown is the shorter path and costs fewer tokens for exactly the same content.
CSV to DOCX, measured rather than promised
Running CSV to DOCX against the real engine with a real file, pandoc wrote 9,945 bytes of DOCX in 0.1 seconds, machine otherwise idle. That is one CSV file on one day and not an average, which is why the number is given together with the file that produced it.
The CSV to DOCX 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 DOCX file has anything inside it.
The same CSV file, sent somewhere else
Other outputs the probe measured out of a CSV file, so the cost of choosing DOCX can be read against something. Sizes do not compare across engines, because each family was probed with its own CSV witness file.
CSV to PDF: 12,680 bytes in 1.0 seconds, verified by a format signature.
CSV to MD: 114 bytes in 0.1 seconds, verified by a pandoc round trip.
CSV to EPUB: 4,913 bytes in 0.1 seconds, verified by a pandoc round trip.
CSV to TXT: 114 bytes in under a tenth of a second, verified by reading the text back.
CSV to HTML: 3,894 bytes in 0.1 seconds, verified by a pandoc round trip.
CSV to RTF: 779 bytes in under a tenth of a second, verified by a pandoc round trip.
Other ways into DOCX, and what they measured
Among the published routes into DOCX, CSV is the eighth largest output of the 12 measured. The witness files differ, so this ranks the probe run and not your document.
JSON to DOCX: 10,106 bytes in 0.1 seconds.
MOBI to DOCX: 24,070 bytes in 0.6 seconds.
PDF to DOCX: 23,905 bytes in 0.9 seconds.
EPUB to DOCX: 10,326 bytes in 0.1 seconds.
ODT to DOCX: 5,514 bytes in 1.1 seconds.
What we will not pretend about CSV to DOCX
A CSV file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A CSV to DOCX 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 CSV to DOCX 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 DOCX 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 CSV file goes through LibreOffice or calibre, both of which genuinely can.
One CSV file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
CSV to DOCX: what people ask
What actually converts my CSV file to DOCX?
pandoc does it, in two passes, on a machine we rent and watch. Not a browser trick and not somebody else service: the CSV file is uploaded once, pandoc runs once, the DOCX comes back, and neither file is kept afterwards.
How long does CSV to DOCX take?
On the file the probe used, pandoc took 0.1 seconds and wrote 9,945 bytes of DOCX. That is one real measurement on one real CSV file, not an average and not a promise about yours: a larger CSV takes longer, and past 60 seconds the run is stopped.
What do I lose going from CSV to DOCX?
The one to know about first: Nothing that was ever there, which is the honest answer for this pair: a CSV file has no page layout to lose. The DOCX you get uses the default Word template, so it is a plain document rather than a designed one.
Are the tables in my CSV file still tables in the DOCX?
Yes. pandoc reads the CSV tables into its own document tree and writes them back out in DOCX syntax, so what you get is a table a machine can parse rather than a picture of one.
Is CSV to DOCX free?
There is a free allowance every month, and one CSV to DOCX 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 DOCX.