LibreOffice Calls Euro-Office a 'De Facto Ally' of Microsoft Over OOXML Default

The Document Foundation, the organization behind LibreOffice, has publicly accused Euro-Office of working against the European digital sovereignty goals it claims to advance. The complaint centers on a technical detail with real compliance consequences: which document format the software saves to by default.

Italo Vignoli, a founding member of The Document Foundation, published an open letter on Monday, hours before Euro-Office 1.0 launched as a self-described "truly open" and sovereign alternative to Microsoft Office. His central charge is blunt. Euro-Office defaults to Microsoft's Office Open XML (OOXML) format, the format that already dominates corporate desktops, and in doing so it reinforces exactly the dependency it claims to break.

"Euro-Office defaults to the fully proprietary OOXML document format, developed and controlled solely by Microsoft," Vignoli wrote. "This makes it a de facto ally of Microsoft in its content lock-in strategy, with control remaining firmly in Redmond and far from Europe."

Why the format choice matters

The technical argument here is more substantive than a branding squabble. Document formats determine who controls your data over the long term. The Open Document Format (ODF) is an ISO-standardized specification, ISO/IEC 26300, maintained through an open process and implemented by multiple independent suites. OOXML, standardized as ISO/IEC 29500 but in practice steered by Microsoft, governs the .docx, .xlsx, and .pptx files most organizations exchange every day.

For an organization pursuing digital sovereignty, the default format is not a cosmetic setting. When a suite saves to OOXML by default, every new document an employee creates becomes part of the Microsoft-controlled ecosystem. Files inherit compatibility expectations that pull users back toward Microsoft tooling, and the organization remains exposed to format changes it does not control. Vignoli's point is that swapping the application while keeping the format leaves the underlying dependency intact.

The sovereignty dispute in context

Vignoli also challenged Euro-Office's marketing claim to being the first European open-source office suite. That distinction, he argued, belongs to OpenOffice.org, released in 2001 from Sun Microsystems' StarOffice codebase, and later to LibreOffice in 2010. His framing positions Euro-Office as a recent entrant in a market that European open-source projects helped build, rather than the pioneer its launch materials suggest.

The friction predates this week. Euro-Office is a fork of the OnlyOffice productivity suite, unveiled in April by German cloud firm Nextcloud and hosting provider Ionos and aimed at organizations seeking European-controlled alternatives to US software vendors. OnlyOffice's original developer objected to the fork and its branding at the time. The Document Foundation's open letter adds a second prominent open-source voice to the criticism.

The broader push matters because European public bodies and enterprises are under increasing pressure to reduce reliance on US cloud and software providers, driven by data-residency concerns and regulatory scrutiny of cross-border data flows. In that climate, a productivity suite branded as sovereign carries weight in procurement decisions.

What Euro-Office's backers say

Euro-Office's creators did not dispute the underlying concern about proprietary formats. A spokesperson told The Register that proprietary file formats are "a serious hinderance to digital sovereignty" and framed the OOXML default as a transitional measure.

"We thus need to free users who are stuck using these formats, and enable them to work with an open office platform. This will allow organizations to transition to open document formats like ODF," the spokesperson said, adding that the project will "focus development efforts on improving ODF support. Ultimately, ODF should be the standard, not OOXML, and we will work towards that."

That response concedes the principle while defending the practical choice. Most users arrive with existing OOXML files, and a suite that cannot open them cleanly is a hard sell. The disagreement is really about sequencing: whether defaulting to OOXML to ease adoption is a reasonable on-ramp or a compromise that quietly preserves the lock-in.

The practical takeaway

For organizations evaluating these tools as part of a sovereignty or data-control strategy, the lesson is to look past the marketing label and check the defaults. The questions that matter are concrete. What format does the suite save to out of the box? Can that default be enforced through administrative policy across an organization? How complete is ODF round-trip support, meaning whether a document survives saving, closing, and reopening without losing formatting?

The dispute between LibreOffice and Euro-Office is a reminder that adopting European-developed software does not automatically deliver format independence. Sovereignty lives in the file format and the data, not only in the vendor's headquarters. Until a suite defaults to an open standard and reliably preserves documents in it, the underlying dependency persists regardless of the name on the box.