PPT is the pre-2007 PowerPoint binary. PPTX is a PowerPoint deck, with slides and speaker notes. LibreOffice sits between the two, and this page says exactly what happens to a PPT file on the way to becoming a PPTX one.
What runs when a PPT file becomes PPTX
LibreOffice 24.2, on a machine we rent and watch. Your PPT file is uploaded once, LibreOffice runs once, the PPTX comes back, and neither file is kept. PPT to PPTX 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 PPT into the PPTX
A PPTX you can still edit. This pair swaps the container, not the content: what comes back opens in a presentation application and takes changes, which is the whole reason to do it rather than print to PDF.
Speaker notes, attached to their slide. They travel with the deck into the PPTX, which is what makes this different from exporting the slides as pictures.
What PPT to PPTX costs you
Exact pagination. PPT and PPTX compute line breaks and page breaks with different engines, so a document that filled four pages can come back filling five. Nothing is missing; it sits elsewhere.
Macros, and anything an application kept to itself. VBA does not cross into ODF and ODF Basic does not cross into OOXML, so a PPT file that automates itself arrives in the PPTX as one that does not.
Animations and slide transitions. The slides, their order and their notes arrive; the movement between them does not.
Where PPT and PPTX files come from
PPT. PowerPoint wrote it before 2007, and it is an OLE2 binary. Decks of this age usually come out of an archive rather than off somebody desk, which is why converting one is generally the first step in reading an old presentation at all.
PPTX. PowerPoint writes it, along with Google Slides and Keynote on export. It is ISO/IEC 29500 like DOCX: a zip of XML, with each slide and each set of speaker notes in its own file inside.
If a model is going to read the PPTX
Structure is what survives from the PPT file, and structure is what a model needs. PPT in, PPTX out, with the heading tree intact instead of flattened into one long paragraph.
PPT to PPTX, measured rather than promised
Running PPT to PPTX against the real engine with a real file, LibreOffice wrote 37,413 bytes of PPTX in 1.2 seconds, machine otherwise idle. That is one PPT file on one day and not an average, which is why the number is given together with the file that produced it.
The PPT to PPTX 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 PPTX file has anything inside it.
The same PPT file, sent somewhere else
Other outputs the probe measured out of a PPT file, so the cost of choosing PPTX can be read against something. Sizes do not compare across engines, because each family was probed with its own PPT witness file.
PPT to PDF: 20,740 bytes in 1.1 seconds, verified by a format signature.
PPT to HTML: 27,543 bytes in 1.5 seconds, verified by reading the internal type and finding a witness word.
Other ways into PPTX, and what they measured
Among the published routes into PPTX, PPT is the second largest output of the 2 measured. The witness files differ, so this ranks the probe run and not your document.
ODP to PPTX: 41,050 bytes in 1.4 seconds.
What we will not pretend about PPT to PPTX
A PPT file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A PPT to PPTX run that passes 90 seconds is killed, and the LibreOffice process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
LibreOffice is serialised on purpose, one document at a time per worker, because each soffice instance takes 150 to 300 MB on a machine with 3.8 GB. Measured ceiling: 23 PPT conversions in flight and roughly 0.9 a second sustained. Past that the queue answers 429 rather than falling over, which was tested at 32 at once.
Two thirds of the pairs you could imagine in this family do not exist, and it is worth knowing why before you go looking for one. LibreOffice converts inside whichever application opened your file: from a spreadsheet it writes spreadsheets, flat text, HTML and PDF, and it will not write a .docx no matter how it is asked. It returns nothing at all rather than something wrong. Of 113 combinations probed on this engine, 64 came back with a real file and the rest were refused outright.
This pair is one of the 64. It was proved by sending a real PPT file through the live route and reading the PPTX that came back: not its extension, its internals, plus a marker word planted in the source and found again in the output. The traits named further up this page come from a second probe that looks for each of them one by one.
One PPT file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
PPT to PPTX: what people ask
What actually converts my PPT file to PPTX?
LibreOffice does it, 24.2, on a machine we rent and watch. Not a browser trick and not somebody else service: the PPT file is uploaded once, LibreOffice runs once, the PPTX comes back, and neither file is kept afterwards.
How long does PPT to PPTX take?
On the file the probe used, LibreOffice took 1.2 seconds and wrote 37,413 bytes of PPTX. That is one real measurement on one real PPT file, not an average and not a promise about yours: a larger PPT takes longer, and past 90 seconds the run is stopped.
What do I lose going from PPT to PPTX?
The one to know about first: Exact pagination. PPT and PPTX compute line breaks and page breaks with different engines, so a document that filled four pages can come back filling five. Nothing is missing; it sits elsewhere.
Can I still edit the PPTX?
Yes, and that is the point of this pair rather than a PDF export. What comes back is a working PPTX: open it, change it, save it. Headings are still headings and tables are still tables, so the document knows what its own parts are.
Will it look identical?
Close, not identical, and the difference is honest. PPT and PPTX lay text out with different engines, so line and page breaks can fall elsewhere and a four page document can come back at five. Nothing is missing when that happens; it sits in a different place. If you need the layout frozen exactly, convert to PDF instead, and accept that you can no longer edit it.
Is PPT to PPTX free?
There is a free allowance every month, and one PPT to PPTX 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 PPTX.