LibreOffice Developer Attacks Microsoft OOXML Again Over Digital Sovereignty

As The Document Foundation developer of LibreOffice, The Document Foundation has once again criticized Microsoft over its Office document formats, arguing that the company’s OOXML format remains proprietary in practice despite being presented as an open standard.

According to a recent statement highlighted by Neowin, the foundation says governments, organizations, and users seeking “digital sovereignty” should adopt ODF, or OpenDocument Format, as their default document standard instead of Microsoft’s OOXML.

LibreOffice pushes ODF as the truly open format

The foundation argues that ODF remains fully open because no single vendor controls how the format evolves. Documents created using ODF stay independent from one company’s ecosystem, which LibreOffice says protects users from vendor lock-in.

By contrast, TDF claims Microsoft’s OOXML format effectively keeps organizations tied to Microsoft Office workflows and infrastructure. The group says that while OOXML is technically documented, its complexity and Microsoft-centric implementation reduce real interoperability.

LibreOffice developers also argue that ODF should become the default native format for productivity software rather than simply being an optional compatibility feature.

TDF criticizes OOXML complexity and standards process

One of the biggest criticisms focuses on OOXML’s size and structure. TDF says the specification exceeds 7,500 pages and lacks proper transparency, independent governance, and version consistency.

The organization also repeated long-standing criticism that OOXML was initially developed behind closed doors at Microsoft before later becoming standardized.

According to TDF, Microsoft originally positioned OOXML as a transitional format that would eventually evolve into a stricter and more open standard. The foundation argues that this shift never fully happened and that Microsoft still benefits from a dominant position over user-created documents.

Excel date handling remains a major complaint

LibreOffice’s developers also highlighted Microsoft Excel’s long-criticized date handling behavior.

Excel famously treats 1900 as a leap year even though it was not one historically. Microsoft has preserved the behavior for compatibility reasons, but TDF argues the workaround reflects unnecessary legacy complexity within OOXML and Office formats.

The foundation also referenced a real-world scientific issue involving gene names. In 2020, the HUGO Gene Nomenclature Committee renamed several genes, including SEPT1 and MARCH1, because Excel frequently converted them into dates automatically.

LibreOffice says the incident demonstrates how Microsoft Office behavior can shape wider scientific and business workflows.

Microsoft and LibreOffice have clashed before

This is not the first public disagreement between LibreOffice and Microsoft. The two sides have repeatedly clashed over document standards, interoperability, and interface design over the years.

LibreOffice previously criticized Microsoft’s Ribbon interface, while supporters of ODF have also pushed governments and public institutions toward open document standards. Some European organizations and institutions have increased ODF adoption in recent years following pressure from open-source advocates.

TDF says relying on OOXML for native document storage creates what it calls “false digital sovereignty,” because users still depend heavily on Microsoft’s ecosystem for full compatibility and functionality.

The Document Foundation argues that true digital sovereignty requires organizations to adopt ODF as their primary document format instead of OOXML. LibreOffice maintains that open standards should remain vendor-neutral, transparent, and fully interoperable across platforms and software ecosystems.