Microsoft 365 Copilot and professional secrecy: what a firm needs to know

Consumer Copilot or Microsoft 365 Copilot: what is the difference?

The name “Copilot” refers to two services that are not governed by the same rules. To complicate matters, in 2026 Microsoft renamed “Microsoft 365 Copilot” to “Microsoft Copilot,” and “Microsoft 365 Copilot Chat” to “Microsoft Copilot Chat.” What matters is therefore not the name displayed, but the account you sign in with.

First rule, simple to apply: no client file goes through a Copilot opened with a personal account, on a colleague's phone or on copilot.com. The document then leaves the firm's contractual framework: no data protection addendum and, with the old version of the app still installed on some computers, possible training and 18-month retention.

Does Microsoft 365 Copilot protect data confidentiality?

Microsoft groups its commitments under the name “Enterprise Data Protection.” According to its documentation, an organization's use of Copilot and Copilot Chat falls under the DPA and the Product Terms, “with Microsoft acting as a data processor.” In practice:

• No training: prompts, responses and data accessible through Microsoft Graph are not used to train large language models, including those used by Copilot.
• Same rules as e-mail: prompts and responses benefit from the same contractual commitments as Exchange e-mails and SharePoint files.
• Your settings apply: Copilot respects access permissions, sensitivity labels and Purview encryption, applies retention policies and allows interactions to be audited. The detail depends on the subscription.
• A stored history: Microsoft stores every prompt and response, with its citations. This history is encrypted, searchable by administrators, and users can delete it from the My Account portal.

These commitments are serious. They answer a GDPR question: Microsoft is a processor bound by a contract, within the meaning of Article 28. On their own, they do not answer the professional secrecy question, which is dealt with below.

Can Copilot expose a file internally? Oversharing

Business Copilot does not invent access rights. Microsoft says so clearly: it only surfaces data that the user has “at least” permission to view. But it finds it in seconds, by cross-referencing e-mails, files and meetings. A file stored in a SharePoint site open to the whole firm, a forgotten “anyone in the organization” link on a OneDrive, an overly broad Teams team: what was impossible to find becomes the answer to an innocuous question.

In a firm, this is a secrecy issue. The employment-law trainee has no business reading the strategy note on a criminal case, nor one partner's associate the litigation of a competing client. Microsoft acknowledges this in its “Secure & Governed Data Foundation” deployment blueprint, whose first pillar is to “fix oversharing,” with the SharePoint Advanced Management tools included in the Copilot license.

Does Copilot data stay in Europe?

For a European customer, Microsoft presents Copilot as an EU Data Boundary service: “European traffic stays within the EU Data Boundary.” Its documentation nevertheless flags two exceptions.

• Web search: when Copilot queries Bing, it turns the prompt into a few search words, without any user or tenant identifier. Bing runs outside Microsoft 365, under the Microsoft Services Agreement and the privacy statement: there, Microsoft acts as an independent controller, and the EU Data Boundary does not apply. A search can therefore contain a client's name if the prompt contains one.
• Anthropic models: Microsoft offers third-party models in Copilot, which the administrator chooses whether to enable. Anthropic's are “currently excluded from the EU Data Boundary.”

An administrator can turn off web search and third-party models. You still need to know this, and check it every time the service changes.

Can a lawyer use Copilot without breaching professional secrecy?

Professional secrecy forbids disclosing information to any third party whatsoever. Article 226-13 of the French Criminal Code (Code pénal) punishes such disclosure “with one year of imprisonment and a fine of 15,000 euros” (our translation). A well-drafted processing agreement governs what the provider does with the data; it does not turn the provider into the client's confidant.

The regulated professions draw the same conclusion:

• Lawyers: the March 2026 guide of the Conseil national des barreaux (French national bar council) sets the principle that no file or client data goes into a generative AI. The detail is in our summary of the CNB guide on AI and in ChatGPT and lawyers.
• Chartered accountants: a booklet from the profession only allows client data in Copilot 365 if the GDPR option is enabled in administration, and warns that its table may have aged. See ChatGPT and chartered accountants.
• Notaries: the notary's secrecy is “general and absolute,” and the CSN (French notaries' council) offers its own AI solution. See AI and notaries.

To prepare these copies, profession by profession: document anonymization software for lawyers, document anonymization software for notaries, document anonymization software for chartered accountants, document anonymization software for in-house counsel and DPOs.

For an overview of the rules by profession, our guide AI and professional secrecy brings the texts together. The practical conclusion is the same everywhere: Copilot is useful for drafting, summarizing and rephrasing, provided you give it a copy in which the client can no longer be recognized.

How do you use Copilot on a client file?

1. Set up the tenant. Entra ID accounts only, no personal accounts for work. Fix oversharing, apply sensitivity labels to client files, decide whether web search and third-party models stay enabled.
2. Prepare the copy outside Microsoft 365. With AnonymFiles, drop in the file: PDFs, scans read through local OCR, Word, .eml and .msg e-mails, Excel, CSV, PowerPoint. Names, organizations, addresses, e-mails, phone numbers, IBANs, private dates and ID numbers are replaced with stable labels such as [PERSONNE_1], on the computer.
3. Review side by side. Each original is shown next to its copy; one click masks an amount, a case number, a forgotten reference. Nothing is exported without approval.
4. Export. A Word file becomes a .docx redacted in place, layout preserved, and a PDF is rebuilt with the content truly deleted. The mapping table is never part of the export.
5. Work with Copilot. Open the copy in Word or paste it into Copilot Chat, with the instruction provided by the app so that the labels stay intact.
6. Re-inject. Bring the answer back into the app: it puts the real names back as text, Word or PDF, on the computer.

On the network side, the app works with no account and no telemetry, and its license is checked on the computer, with no network call. On Mac, the detection models are included; on Windows, they are downloaded once at the first processing run, without any document text. The security page details what the app does and does not do on the network. Pricing: €290 excl. VAT per seat per year for one or two seats, €240 excl. VAT per seat from three seats, quote above twenty seats.