Convert PPT to PPTX

This conversion is for a deck with a future rather than one being filed. A training course is being refreshed for a new intake and the slides are still mostly right. A lecture series is being picked up by whoever inherited the module. A conference template, a sales deck, an induction pack, a set of technical diagrams somebody drew carefully in 2004 and nobody wants to redraw. The content is worth keeping and it has to be editable, which rules out a PDF.

What stops people is rarely PowerPoint itself — the desktop program still opens a `.ppt` unless an administrator has switched it off. It is everything around it: a Trust Center file-block policy, a mail gateway, an upload form that lists `.pptx` and nothing else, a learning management system, Teams or Google Slides refusing a format they never implemented. Converting once puts the deck on the right side of all of those at the same time.

The registry dates PPT to 1990 and marks it legacy, structured as a binary file. It is an OLE compound file: a small filesystem inside a file, with named streams holding the slides, the master, the embedded objects and, if present, the VBA project. Everything is stored uncompressed and the structure is opaque without a library that understands it.

PPTX is from 2007 and standardised as ECMA-376. It is a ZIP archive containing XML — one part per slide, parts for the masters and layouts, a theme, a relationship graph, and the pictures as ordinary image files in a media folder. You can unzip one and read it, which matters more than it sounds: a deck that has gone wrong can be inspected, and a batch of decks can have the same fix applied by script. It is also why the file is usually smaller, since XML compresses extremely well.

The substance of the deck. Slide text, titles, bullet levels and their formatting; shapes and their fills, lines and positions; tables; pictures; slide masters and layouts; speaker notes; hyperlinks; headers, footers and slide numbering; the deck’s dimensions and orientation. Charts drawn with PowerPoint’s own tools generally arrive as charts.

The work is done by LibreOffice, which reads the binary PowerPoint format as a first-class filter and writes PPTX the same way, and the machine it runs on carries metric-compatible substitutes for Arial, Times New Roman, Courier New, Calibri and Cambria. Those have the same character widths as the originals, so a text box that held three lines still holds three lines rather than overflowing. That matters more on slides than in documents, because a slide has no reflow — text that grows by one line does not push the next paragraph down, it runs off the bottom of the box.

A `.pptx` is forbidden to hold a VBA project. Microsoft split the extensions in 2007 precisely so that software could tell a file that might run code from one that cannot, and a macro-bearing deck has to be saved as `.pptm`. So converting strips whatever automation the old deck carried.

On a deck from the binary era that is nearly always a benefit rather than a loss. Macros in presentations were uncommon and were usually a navigation gimmick — a button that jumped to a section, a self-advancing loop, a quiz that scored itself — and the same effect is now available through hyperlinks and action settings without any code. If the file has ever produced a security warning on opening, this conversion is the clean answer to it, and it is very likely the reason the mail gateway was refusing the attachment.

The binary format could embed a live object from another application: a chart pasted from Excel 97, an equation from Microsoft Equation 3.0, an organisation chart from the tool that shipped with Office 2000, a Visio drawing, a Word table. Each of those was stored as a stream that only the originating program could edit, and several of those programs have been gone for over a decade — Equation 3.0 was removed from Office entirely in 2018 for security reasons.

Expect them to arrive as pictures. That is the right outcome and it is worth knowing in advance: the object will look correct on the slide and double-clicking it will no longer open anything. If a chart needs to be updated with new figures, it has to be rebuilt as a native PowerPoint chart, and the conversion is the moment to find that out rather than the morning of the presentation. Equations are the case to check first, because an unreadable formula is not something an audience forgives.

PowerPoint 2007 replaced the animation engine, and that is the single largest source of difference in this conversion. Simple effects have direct equivalents and survive: appear, fade, fly in, wipe, and the standard slide transitions. Timings that were straightforward remain straightforward.

Custom animation built in the 2003 interface is where the mapping gets loose — motion paths, chained sequences with delays, effects applied to individual chart series or table rows, and anything relying on the old timeline. The result is usually a simplification rather than a failure, but a slide whose meaning depends on the order things appear in deserves a look. Run the deck once in presentation mode after converting; it takes as long as the deck does and it is the only check that tests the thing that actually breaks.

A document reflows and a slide does not. When a substituted font is slightly wider, a paragraph in Word pushes the next one down and the document gets a page longer; a title on a slide runs past the edge of its box, over the image, or off the slide entirely. Old decks are particularly exposed because 1990s and 2000s house styles leaned on faces that were installed with the software of the day.

The converter’s metric-compatible substitutes cover the common Microsoft faces, so most decks hold their layout. What they cannot cover is a licensed brand typeface or something downloaded once and long forgotten. Open the PPTX and look at the titles across every slide, not just the first three — a title is the text most likely to have been set at a size chosen to just fit. Where a deck is going to be reused for years, this is also the moment to replace an unavailable face with one that will still exist next time.

On our server, not in your browser. Reading a binary PowerPoint file needs a real office engine, and this page says so plainly rather than implying that everything on this site runs on your own device. The file travels over an encrypted connection to a container running LibreOffice headless, and the container has no outbound internet access of its own.

Each job gets its own scratch directory and its own LibreOffice profile — two `soffice` processes sharing a profile corrupt it, and the symptom is a conversion that never returns rather than an error — and the directory is deleted when the job ends whatever the outcome. Anything still running after sixty seconds is terminated, which matters for legacy binaries in particular: LibreOffice tends to stop rather than fail on a malformed old file. The free tier accepts 25 MB per uploaded file.

Go through it in slide sorter view first, which shows every slide at once and makes the two common failures obvious immediately: a slide where text has overflowed its box, and a slide where a former embedded object has become a picture at the wrong size. Both are quick to fix and both are much cheaper to fix now than in front of an audience.

Then present it end to end once. That is the only way to test the animation and the transitions, and it is also how you find the slide that used to be built in five clicks and now arrives complete. If the deck is one of a set produced from the same template, the failures will repeat, so a careful review of one deck tells you what to fix in all of them. Keep the original `.ppt` until the new version has been presented once — it is the only record of what the deck was, and no conversion is worth losing that over.