I've been writing about sovereignty washing all summer. The pattern is consistent: AWS puts a German GmbH around its data centers and calls it a European Sovereign Cloud. The CLOUD Act still applies. Canada's federal government spends $2.36 billion on "sovereign" infrastructure procured from Canadian corporations. The sovereignty is in the procurement contract, not the architecture.

The document format fight is the same argument one layer down. You can self-host Nextcloud on a server in your fire hall. You can run it on hardware you own, on Proxmox you control, with encryption keys you hold. If the files your community creates are stored in a format controlled by Microsoft, you've relocated the dependency. You haven't removed it.

That's The Document Foundation's argument. It's correct. It's also incomplete, and the incompleteness matters.

What Euro-Office Actually Is

Euro-Office is a browser-based office suite — document editor, spreadsheet, presentation tool, PDF editor — built by a European tech industry alliance. It shipped as part of Nextcloud Hub 26 Spring on June 9, 2026, Nextcloud's 10th anniversary release.

The technical implementation is specific. Euro-Office uses a clean-room OOXML implementation. That means they wrote their own code to read and write Microsoft's file formats (DOCX, XLSX, PPTX) from the published specification, without using Microsoft's reference code. It also supports ODF equivalents (ODT, ODS, ODP). Real-time collaborative editing is built in. Version 1.0 has no desktop or mobile clients — those are on the roadmap.

The key phrase is "clean-room OOXML implementation." Full OOXML fidelity is a work in progress. Documents with complex macros or advanced formatting show a warning if they can't render faithfully. This is an honest v1.0: functional, usable, not feature-complete.

Nextcloud users now have a choice of two office suites: Euro-Office or Collabora Online. Both are supported. Collabora Online is built on LibreOffice Technology, which is built around ODF.

The Document Foundation's Critique

The day before Euro-Office launched, The Document Foundation published an open letter calling it "a de facto ally of Microsoft in its content lock-in strategy." Italo Vignoli, TDF co-founder, expanded the argument in an August 18 piece on FOSS Force titled "Digital Sovereignty Without Open Standards Spells Defeat."

The argument has three layers.

Layer 1: OOXML Transitional is not an open standard. The version of OOXML every proprietary vendor ships by default is the Transitional conformance class, not the cleaner Strict variant. OOXML Transitional was designed to preserve decades of undocumented legacy behavior from Microsoft Office versions of the 1990s. It is a specification only one vendor has ever fully implemented. An office suite that treats OOXML Transitional as its working format is building on a foundation controlled by Microsoft, regardless of where the servers sit.

TDF published a 13-criterion definition of what a genuinely open document format requires: public specification, royalty-free implementation, independent governance, multi-vendor implementation, and nine more. They're applying it to ODF, OOXML Strict, and OOXML Transitional in a forthcoming detailed analysis. The short version: ODF passes. OOXML Strict is debatable. OOXML Transitional fails.

Layer 2: Format control cascades into dependency. A document format is not just a file extension. It determines which rendering engine can display the file faithfully, which fonts produce the correct output, and which tools can process the data. TDF calls this "the invisible architecture of lock-in" — five layers deep, from the file format through the rendering engine, the fonts, the migration deadline a vendor sets, and the subscription price it charges. At every layer, the user has no exit.

If your community's records are in DOCX, you need a tool that reads DOCX faithfully. If "faithfully" means "exactly like Microsoft Word renders it," you need Microsoft Word — or a compatibility layer that's always playing catch-up. The format is the dependency.

Layer 3: Governance is sovereignty. LibreOffice Technology is governed by The Document Foundation, a German non-profit whose statutes prevent any single company from controlling the foundation. The codebase is MPL 2.0 licensed — it can never be made proprietary. No acquisition can change the license. No pricing decision by a distant board can determine whether your organization can keep using it next year.

Euro-Office is built by a coalition. The governance structure is newer and less tested. The question TDF raises is structural: if the coalition dissolves, who controls the code? If a member company leaves, what happens to the roadmap? TDF's answer is that they solved this problem in 2010 when they split from Oracle's OpenOffice.org, and the solution is statutory independence — not good intentions.

The Counter-Argument Nextcloud Actually Has

TDF's critique is technically correct and practically incomplete. Here's the part they don't dwell on.

ODF has existed since 2006. It's been an ISO/IEC international standard (ISO/IEC 26300) for two decades. In those 20 years, it has not achieved mainstream adoption outside of governments that mandated it. Microsoft 365 runs the office software market. Google Workspace runs the rest. Both default to OOXML or proprietary formats. The vast majority of documents created on Earth in the last 20 years are DOCX, XLSX, or PPTX.

If you're running a community organization — a town office, a fire hall, a small nonprofit — your members send you .docx files. Your board minutes were written in Word. Your grant applications require .docx uploads. Your accountant sends .xlsx spreadsheets. ODF is technically superior for sovereignty. It is practically useless if it can't open the files your community actually has.

Euro-Office's bet is that OOXML compatibility is the migration path. You can't move people off Microsoft 365 if your tool can't open their existing documents without conversion friction. A clean-room OOXML implementation that renders DOCX faithfully in a browser, bundled into a self-hosted Nextcloud, is the most credible "first step" toward sovereignty for organizations that are not going to start by converting 15 years of .docx files to .odt.

This is the same argument as Collabora Online's, but with a different default. Collabora Online also reads and writes OOXML. The difference is that Collabora Online's native format is ODF — OOXML is a compatibility layer on top of a platform built around ODF. Euro-Office's native format appears to be OOXML, with ODF as a supported option.

That distinction is what the fight is about.

What Governments Actually Decided

The deployment evidence is where the argument gets concrete.

Germany chose ODF. In March 2026, Germany's Federal Ministry for Digital and State Modernization folded ODF — alongside PDF/UA — into the Deutschland-Stack, the technical framework governing digital infrastructure across every level of German public administration. OOXML did not make the list. Florian Effenberger, TDF's Executive Director, was explicit: "This is not a recommendation or a preference, it is a mandate."

The Austrian military chose LibreOffice. In an August 2026 interview with TDF, the Austrian Armed Forces described moving 16,000 workstations off Microsoft Office. The decision traced to a 2020 review of what guarantees existed for running office software without a cloud connection. They needed software that works offline, on their own hardware, with no vendor phone-home. LibreOffice met that. Microsoft Office did not.

Italy chose LibreOffice. The Italian Ministry of Defence's LibreDifesa program has migrated over 100,000 workstations to LibreOffice over several years.

France chose open source. The French National Gendarmerie has spent two decades moving the substantial majority of its computing estate to open-source software, including LibreOffice, as deliberate vendor lock-in reduction.

These are not pilots. They are operational deployments in organizations where controlling the software stack is a security and continuity requirement, not an ideological preference. All four chose LibreOffice Technology and ODF. None chose a compatibility-first approach.

The pattern is consistent: when the decision is made by people responsible for sovereignty — military, government, national security — they choose the format nobody controls over the format one vendor controls. When the decision is made by people responsible for migration — getting users off Microsoft 365 with minimal friction — the calculus shifts.

What Your Community Should Actually Do

The practical question for a community deploying Nextcloud is not "ODF or OOXML" as an either/or. It's about defaults and migration paths.

Default to ODF. Store in ODF. When your Nextcloud instance creates a new document, it should default to ODF. When someone uploads a .docx, Euro-Office or Collabora should open it — but the saved version should be ODF unless the user explicitly chooses otherwise. This is how you move the needle: not by requiring conversion of 15 years of historical documents, but by making sure every new document is born sovereign.

Use OOXML as a compatibility layer, not a storage format. Both Euro-Office and Collabora Online read and write OOXML. That's necessary for migration. It is not a reason to make OOXML your working format. Open .docx files. Edit them. Save them as .odt. The compatibility is a tool, not a destination.

Prefer Collabora Online for now. If you're deploying Nextcloud for a community today, Collabora Online is the more mature choice. It's built on LibreOffice Technology, it has desktop and mobile support, its native format is ODF, and its governance is proven. Euro-Office is a real v1.0 — functional but not feature-complete, no desktop/mobile clients yet, and the OOXML-default architecture is a legitimate concern. Watch Euro-Office. Don't deploy it as your primary office suite yet.

Understand the five layers. TDF's "invisible architecture of lock-in" framework is useful even if you disagree with TDF's conclusions. The layers are: file format, rendering engine, fonts, migration deadline, subscription price. At each layer, ask: can I exit without losing my data or my ability to work? If the answer is no at any layer, that's where the dependency lives. A self-hosted Nextcloud running Collabora Online with ODF storage gives you an exit at every layer. A self-hosted Nextcloud running Euro-Office with OOXML storage gives you an exit at the hosting layer and a question mark at the format layer.

The Real Disagreement

TDF and Nextcloud are not arguing about whether sovereignty matters. They agree it does. They're arguing about what counts.

TDF says: a format controlled by one vendor is not sovereign, no matter who runs the server. If the format is OOXML Transitional, Microsoft controls the evolution of your file format. Sovereignty requires ODF.

Nextcloud says: a tool that can't open the files your community actually has is not a migration path, it's a wall. Sovereignty that nobody can reach is not sovereignty. OOXML compatibility is the bridge.

Both are right. The resolution is not to pick a side. It's to separate the migration from the destination. Use OOXML compatibility to get people in the door. Store in ODF. Make ODF the default. Treat OOXML as an interchange format, not a storage format.

Germany, Austria, Italy, and France already made this decision. They chose ODF. They did not choose it because OOXML is hard to read. They chose it because the question of who controls your file format in ten years is a sovereignty question, and the answer "a single vendor in Redmond" is not sovereign — no matter how many European servers you put in front of it.

The same logic that applies to your Proxmox cluster applies to your document folder. You own the hardware. You own the keys. You should own the format.