The Document Foundation (TDF) fired a warning shot in two directions on July 17, 2026. Its message: Microsoft’s default Office Open XML formats still lock users into the tech giant’s orbit, and a new European “sovereign” office suite called Euro-Office is a freeware clone that makes the lock-in worse while introducing questionable ties to Russian developers.

TDF, the nonprofit steward of LibreOffice, detailed its concerns in a blog post accompanied by a technical paper. The core argument is not new, but it has gained fresh urgency as EU-backed alternatives like Euro-Office—marketed as a digital sovereignty tool—end up reinforcing the very dependency they claim to break.

The Double Warning from LibreOffice’s Steward

At the heart of the criticism lies the distinction between two flavors of the ISO/IEC-standardized OOXML format: Transitional and Strict. Microsoft Office defaults to OOXML Transitional, a specification bloated with legacy compatibility behaviors and proprietary quirks that make complete independent implementation a herculean task. OOXML Strict, a cleaner conformance class stripped of those legacy constructs, has never been the default save option and, TDF asserts, isn’t even consistently offered across Microsoft 365 editions.

“A standard that only one implementation fully supports remains proprietary in practical terms,” the foundation wrote. It coined the term “silent friction” for the subtle document corruption that occurs when a .docx or .xlsx file is opened in LibreOffice or another non-Microsoft suite: a shifted table, an altered heading, a broken slide layout. The document opens, but the user’s confidence evaporates, keeping them tethered to Office.

But the July 17 broadside added a new target. In a separate open letter, TDF founding member Italo Vignoli lambasted Euro-Office, an office suite launched earlier this year by a consortium of European tech firms—including IONOS, Nextcloud, and XWiki—as a “sovereign replacement for Microsoft Office.”

Vignoli called Euro-Office a blatant “freeware clone” of Microsoft Office. Its sin, according to TDF, is that it apes Microsoft’s interface and, worse, defaults to the same proprietary-leaning OOXML format. “Euro-Office defaults to the fully proprietary OOXML document format,” the letter stated, arguing that this simply reinforces Microsoft’s ecosystem and creates long-term dependency.

The criticism didn’t stop at file formats. Cybernews published an investigation revealing that up to 99% of Euro-Office’s codebase traces back to developers working in Russian time zones. Euro-Office is a fork of OnlyOffice, a product originally developed by a Latvian company with deep Russian roots; the European consortium forked it only in March 2026. Yet the new project continues to merge selected code changes from the upstream branch, maintaining a dependency on developers based in Russia. For a suite touted as a pillar of European digital sovereignty, the optics are troubling, and the security implications for governments and regulated industries are impossible to ignore.

The Practical Pain of ‘Silent Friction’

For the typical Windows user, the OOXML issue manifests as maddening interoperability glitches. A résumé with a carefully formatted layout might lose its header styling when opened in LibreOffice. An accountant’s spreadsheet with intricate formulas and pivot tables may calculate correctly but look scrambled. These aren’t theoretical failures; they are the everyday experience of anyone trying to escape the Microsoft tax.

TDF describes this as a “governance and archiving” problem for organizations, not just an annoyance. A legal form, clinical template, or government record that must render precisely across decades is a poor candidate for a format tightly coupled to one vendor’s interpretations. Imagine opening a twenty-year-old .doc file today in modern Word—sometimes it works, and sometimes you regret not converting it to PDF/A when you had the chance.

For the system administrator managing a fleet of Windows devices, the warning is a reminder to classify documents by purpose. Day-to-day collaboration on a contract draft probably won’t suffer from staying in .docx, especially if everyone uses the same Office build. But when that contract becomes a finalized record, the format choice changes from convenience to compliance. Financial services, healthcare, and public-sector admins already know this; TDF’s campaign simply amplifies the message.

A European Office Suite Under Fire

Euro-Office was meant to answer a perennial question: Can Europe produce a viable, sovereign alternative to Microsoft Office that governments and businesses can trust? The answer, according to TDF, is a resounding “no”—at least in its current form.

By defaulting to OOXML, Euro-Office does exactly what Microsoft wants: it normalizes the format and keeps documents circulating within an ecosystem that the Redmond company ultimately controls. “If a sovereign office suite adopts the same proprietary format as the dominant vendor, it becomes a de facto ally of vendor lock-in,” Vignoli’s letter implied. The familiar ribbon interface, while easing migration, also conditions users to expect an Office-like experience, making it harder to ever switch to a genuinely open alternative like LibreOffice.

Then there are the Russian ties. OnlyOffice began in Latvia but was built by developers who, according to Cybernews, have largely remained in Russia. Even after the March 2026 fork, Euro-Office still pulls upstream changes, meaning Russian-written code regularly flows into what European governments might install on sensitive networks. In the current geopolitical climate, that’s a red flag for anyone prioritizing sovereignty beyond mere branding.

TDF didn’t hesitate to contrast Euro-Office with its own pedigree: “OpenOffice.org and LibreOffice are two genuine open-source office suites, built from source code that originated in Europe.” The implication is clear—if you want a truly European office suite, you already have it.

How We Got to Yet Another Format Fight

The battle over OOXML dates back to its contentious ISO/IEC standardization in 2008, when critics blasted the process as rigged in Microsoft’s favor. Over the intervening years, TDF has consistently pushed the OpenDocument Format (ODF) as the open standard nations should adopt. It scored a symbolic victory when the UK government listed ODF as a recommended standard, and more recently when the European Commission urged member states to use open formats.

Euro-Office emerged in 2026 from a consortium aiming to create a drop-in replacement that would wean Europe off Microsoft. It bet on familiarity: a cloned interface and OOXML compatibility. But that strategy, TDF argues, is precisely what perpetuates the problem. Instead of breaking the cycle, Euro-Office gives it a fresh coat of paint.

Adding fuel to the fire, Windows Central and Neowin noted that this isn’t TDF’s first attempt to highlight these concerns. The foundation has run multiple campaigns against office initiatives that default to OOXML. The July 2026 salvo simply widened the battlefield to include wannabe competitors that TDF sees as wolves in sovereign sheep’s clothing.

What Windows Users and Admins Should Do Right Now

You don’t need to convert every existing Office document. Microsoft’s formats remain the de facto collaboration standard across most industries. But you can take practical steps to reduce long-term risk.

Check your default format
In Microsoft Word, Excel, or PowerPoint, go to File > Options > Save. The “Save files in this format” dropdown reveals whether you’re committing everything to OOXML Transitional. If your organization has a document retention policy, this setting should be configured via Group Policy or Microsoft 365 admin center to match compliance needs.

Distinguish editable documents from final records
For active, collaboratively edited files, OOXML is often the path of least resistance. Once a document reaches a final state—a signed contract, an archived report—export it to PDF/A for static preservation. The ISO-standard PDF/A format guarantees visual fidelity for decades, independent of application vendor.

If you use ODF for archival, test thoroughly
Switching an existing .docx repository to .odt without validation invites the very corruption TDF warns about. Maintain a reference rendering for high-consequence templates: open the ODF version in LibreOffice, print to PDF, and compare it side-by-side with the Office-originated PDF. Standardize approved fonts (Liberation, Noto, etc.) that exist in both ecosystems.

Vet Euro-Office with extreme caution
If your organization is considering Euro-Office as a sovereignty play, demand a transparent software bill of materials. Verify what proportion of the code originates from Russian contributors and how upstream merges are reviewed. For government or regulated environments, the security vectors are too numerous to ignore. Remember that LibreOffice and Collabora Office already provide open-source alternatives with European provenance and no Russian dependencies.

For IT admins: automate format checks
Scripts can scan network shares for default OOXML extensions and alert when older binary formats (.doc, .xls) appear, which carry even greater lock-in and macro security risks. Microsoft’s own documentation confirms that format conversions can alter formatting and feature behavior, so plan any bulk migration with careful rollback plans.

The Format Battle Is Far from Over

TDF’s double-barreled warning changes little in the immediate landscape. Microsoft will not make OOXML Strict the default tomorrow; its business model depends on a healthy dosage of lock-in. Euro-Office may tweak its defaults under pressure, but its identity is tied to Microsoft compatibility. The real movement will come from regulators and large public-sector buyers who can mandate open formats at procurement time.

Keep an eye on the European Commission’s evolving interoperability guidelines and on any national-level shifts toward ODF mandates. Meanwhile, the quiet work of document format testing inside organizations will matter more than any vendor’s press release. The choice of a file format is ultimately a governance decision, not a religious one—and the July 2026 warnings are a nudge to make that decision actively rather than sleepwalk into a digital monoculture.