The Document Foundation says Microsoft's file formats keep users on a short leash

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The Document Foundation says Microsoft's file formats keep users on a short leash

OOXML may carry an ISO certificate, but only Office can be trusted to render it properly

Richard Speed

Richard<br>Speed

MICROSOFT ECOSYSTEM REPORTER

Published<br>mon 20 Jul 2026 // 17:01 UTC

The Document Foundation (TDF) has criticized proprietary file formats and the lock-in they create, with Microsoft's ubiquitous Office formats drawing particular scrutiny.<br>TDF would doubtless welcome a world where everyone used LibreOffice or another open equivalent, yet the reality is that Microsoft's productivity tools still dominate the office software market.<br>However, that shouldn't be a problem. Files are interchangeable these days, right? Office uses the Office Open XML (OOXML) format, so switching applications and opening .docx, .xlsx, and .pptx files should be straightforward.

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"The reality is considerably more complicated," TDF says.

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Setting aside the standardization of OOXML itself, which, TDF states, "was one of the most contested processes in the history" of the International Organization for Standardization (ISO), the result was OOXML Transitional, which initially coexisted with OOXML Strict.<br>OOXML Strict, according to TDF, eliminated most of the problematic legacy elements, "but not all." Microsoft, on the other hand, defaulted to OOXML Transitional, tucking Strict at the end of the options list.<br>"The practical effect is that the format used daily by hundreds of millions of people is the one that only Microsoft's own software implements correctly, whilst the cleaner variant – which other software could actually support – is not used, and has now even disappeared from some versions."<br>TDF acknowledges the counterargument that the "lock-in" claims are exaggerated and that, for all the controversy surrounding its standardization, OOXML is as open a standard as any other.<br>But TDF disagrees: "A standard that only one implementation fully supports is, from a functional point of view, a proprietary format with a standardisation certificate."<br>The OOXML specification, which runs to thousands of pages, "did not describe a format designed for interoperability, but rather the existing behaviour of Microsoft Office, including legacy behaviours, undocumented features and implementation details specific to Microsoft's source code," TDF claims.

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Document lock-in has to be a factor in sovereignty considerations. "A truly independent document, one that displays identically on any system, in any country, for any user, regardless of the software used – requires informed choices at every stage of its creation."<br>These include the format – TDF gives the example of the OpenDocument Format, used natively in LibreOffice – and even fonts to avoid a dependency on an application that might drop out of support, leaving documents effectively orphaned. Just ask anyone looking glumly at the upcoming demise of Microsoft Publisher and wondering what will become of their files.

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We wondered how an organization would cope with a legacy of thousands, or even millions, of documents. Italo Vignoli of TDF told us there were a few options - use a script and LibreOffice to do a bulk convert and then manually check for interoperability issues, only convert documents needed on a regular basis and send the rest to PDF, or a combination of the two.<br>The latter, Vignoli said, "is usually the chosen one for large organizations, as the first two are often difficult or impossible because of the size (and therefore the number of offices and people involved)."<br>There are plenty of consultants and individuals able to advise on best practise (Vignoli cited experience from migrating half a million seats from Microsoft Office to LibreOffice) but the habit of relying on proprietary tools and formats can be a difficult one to break.<br>"When an institution sends a letter formatted with a proprietary font, embedded in a proprietary format, produced by proprietary software, it is not communicating information but perpetuating a dependency," TDF says.<br>"Digital sovereignty begins with the recognition that this is a choice: the file format is a choice, the font on the page is a choice, and the software is a choice."<br>The Register contacted Microsoft for its take on file formats that lock in users, but aside from acknowledging the question, the company has yet to respond. ®

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