TXT is plain text, with no markup of any kind. PDF is a frozen page layout with no heading structure a machine can rely on. calibre sits between the two, and this page says exactly what happens to a TXT file on the way to becoming a PDF one.
What runs when a TXT file becomes PDF
calibre the ebook-convert binary, on a machine we rent and watch. Your TXT file is uploaded once, calibre runs once, the PDF comes back, and neither file is kept. TXT 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 TXT into the PDF
The reading order and the chapter split of the TXT file. calibre rebuilds it as a book on the way to PDF, rather than as a pile of pages.
Images from the TXT file, placed inline in the PDF where the text refers to them.
What TXT to PDF costs you
Your page breaks, because a TXT file never had any. calibre reflows the text first and computes PDF pages from the result, so where a page ends is the engine decision and not the author one.
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 TXT file, convert it to Markdown instead and skip the reconstruction entirely.
TXT to PDF, measured rather than promised
Running TXT to PDF against the real engine with a real file, calibre wrote 12,976 bytes of PDF in 1.8 seconds, machine otherwise idle. That is one TXT file on one day and not an average, which is why the number is given together with the file that produced it.
The TXT 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 TXT file, sent somewhere else
Other outputs the probe measured out of a TXT 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 TXT witness file.
TXT to MD: 210 bytes in 0.1 seconds, verified by a pandoc round trip.
TXT to DOCX: 9,900 bytes in 0.1 seconds, verified by a pandoc round trip.
TXT to EPUB: 4,955 bytes in 0.1 seconds, verified by a pandoc round trip.
TXT to HTML: 3,896 bytes in 0.1 seconds, verified by a pandoc round trip.
TXT to RTF: 484 bytes in under a tenth of a second, verified by a pandoc round trip.
TXT to ODT: 6,941 bytes in 0.1 seconds, verified by a pandoc round trip.
Other ways into PDF, and what they measured
Among the published routes into PDF, TXT is the number 17 largest output of the 26 measured. The witness files differ, so this ranks the probe run and not your document.
JPG to PDF: 4,232 bytes in under a tenth of a second.
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.
What we will not pretend about TXT to PDF
A TXT file over 50 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A TXT to PDF run that passes 120 seconds is killed, and the calibre process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
The TXT file used to prove this pair was short. calibre is allowed 120 seconds and a long book can genuinely need all of them, so the PDF timing below is a measurement of one small file and not a guarantee about your thousand page one.
One TXT file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
TXT to PDF: what people ask
What actually converts my TXT file to PDF?
calibre does it, the ebook-convert binary, on a machine we rent and watch. Not a browser trick and not somebody else service: the TXT file is uploaded once, calibre runs once, the PDF comes back, and neither file is kept afterwards.
How long does TXT to PDF take?
On the file the probe used, calibre took 1.8 seconds and wrote 12,976 bytes of PDF. That is one real measurement on one real TXT file, not an average and not a promise about yours: a larger TXT takes longer, and past 120 seconds the run is stopped.
What do I lose going from TXT to PDF?
The one to know about first: Your page breaks, because a TXT file never had any. calibre reflows the text first and computes PDF pages from the result, so where a page ends is the engine decision and not the author one.
Does the table of contents survive from TXT to PDF?
It does, as long as your TXT file has real headings rather than text that merely looks like headings. calibre builds the PDF contents from the heading structure it finds, and hand-formatted big bold lines are not a structure.
Is TXT to PDF free?
There is a free allowance every month, and one TXT 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.