[BUG] Claude Desktop (Windows MSIX) registers itself as handler for .docx/.pdf/.csv and becomes default with no opt-out
Preflight Checklist
- [x] I have searched existing issues and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code
What's Wrong?
After a recent Claude Desktop update on Windows 11 (MSIX / Microsoft Store install), the app registered file associations for common document types (.doc, .docx, .csv, .epub, .pdf and others). On machines with no other handler for these types, Windows automatically makes Claude the default, so desktop icons changed to the Claude logo and double-clicking opens Claude.
This happened without any prompt or consent. Windows Settings offers no "no app" option, and deleting the UserChoice registry key doesn't help because Claude is the only registered handler. The only workarounds are editing the package's FileAssociations registry key (which gets recreated on every update) or uninstalling the app.
Request: add a setting to opt out of file type registration, or ask for consent during install/update. Registering as a document handler has no functional value for users who don't want to open documents in Claude.
Environment: Windows 11, Claude Desktop (Microsoft Store/MSIX), September 2026.
What Should Happen?
Claude Desktop should not register file type associations without user consent, or should provide a setting to opt out. Existing file associations (or the absence of any) should remain unchanged after installing or updating the app.
Error Messages/Logs
Steps to Reproduce
- On Windows 11, install or update Claude Desktop (Microsoft Store / MSIX) on a machine with no other application associated with .docx (or .csv, .epub, .pdf).
- Open Settings > Apps > Default apps > Claude: .csv, .doc, .docx, .epub (and others) are listed as handled by Claude.
- Look at any .docx file on the Desktop: it now shows the Claude icon and opens in Claude on double-click.
- Attempt to remove the association: Windows offers no "no app" option; deleting HKCU\...\FileExts\.docx\UserChoice results in Windows re-selecting Claude as the only registered handler.
Claude Model
None
Is this a regression?
Yes, this worked in a previous version
Last Working Version
_No response_
Claude Code Version
Claude Desktop for Windows (Microsoft Store/MSIX), latest version as of 2026-09-03. This concerns the Desktop app, not the Claude Code CLI.
Platform
Anthropic API
Operating System
Windows
Terminal/Shell
Windows Terminal
Additional Information
_No response_
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3 Comments
This happened to me as well. It has taken over associations for .json, .md, .epub, .yml, .text, etc.
It also registered itself as a handler for .jpg, .png, .gif, every Office extension, etc.
The update was automatic, there was no options screen where I chose this, and it is not listed in the changelog. There is no method to stop this from happening in the Claude Code settings that I can find.
This is not acceptable, you can't just take over people's extensions.
I had Claude itself diagnose and this is what it wrote for me:
Confirming this bug, with the full scope of the registration.
Claude Desktop for Windows (MSIX package Claude_1.44121.4.0_x64__pzs8sxrjxfjjc, Windows 11) registers itself as a file handler for 27 extensions, per the package's registration at HKCU\Software\Classes\Local Settings\...\AppModel\Repository\Packages\<package>\Claude\Capabilities\FileAssociations:
.csv, .doc, .docx, .epub, .gif, .jpeg, .jpg, .json, .log, .markdown, .md, .odt, .pdf, .png, .ppt, .pptx, .rtf, .text, .tsv, .txt, .webp, .xls, .xlsm, .xlsx, .xml, .yaml, .yml
For any extension with no existing default (in my case .json, .md, .markdown, .text, .tsv, .yml, and .epub), Windows silently promotes Claude to the default — icons change and double-click opens Claude. This happened with no prompt, no consent, and no mention in the changelog.
There is no opt-out: Windows Settings offers no "no app" option, no UserChoice key exists to reset for these extensions, and removing Claude's AppX… values from OpenWithProgids and the package's FileAssociations key is undone because the registration is recreated on app updates (the package key is version-stamped per update).
Workaround for anyone else affected: explicitly set a default for each hijacked extension (right-click → Open with → choose an app → "Always"). A user-set UserChoice survives Claude's re-registration on update.
Request: don't register document/image file associations at all, or make registration opt-in. There is no scenario where these files need to open in Claude by default.
Confirming this on Windows 11 Pro (Build 26200), Claude Desktop MSIX
Claude_1.46388.4.0_x64__pzs8sxrjxfjjc(2026-09-05 update).Same as reported: the package registers 27 extensions via Capabilities\FileAssociations; the 7 with no existing default (.md, .markdown, .json, .yaml, .yml, .text, .tsv) were silently promoted to Claude as the effective default — icons changed and double-click opened Claude, with no prompt or consent.
Verified on my machine: the update at 12:19 rewrote all
OpenWithProgidsentries at 12:30 (batch-written, same-second registry timestamps), recreating the associations after they had been manually removed — so this recurs on every update, exactly as the issue describes.Like others here: this is outright icon and file-association hijacking. Registering as handler for documents, spreadsheets, and images by default, with no opt-out and no changelog entry, is not behavior I'd expect from a major software company. Please add an opt-out setting (or make registration opt-in) and stop silently re-registering on every update.
Workaround for anyone affected: right-click → Open with → choose your app → "Always" (UserChoice survives re-registration), plus deleting the AppX values from
HKCU\Software\Classes\<ext>\OpenWithProgidsfor the rest.