Symptoms
- Files always open in the wrong app despite changing settings
- Default app resets back after a while
- 'Open with' menu doesn't offer the app you want
- Setting appears saved but doesn't take effect
Likely causes
- CommonAnother app re-claims itself as default after an updateSome apps reset file associations automatically when they update.
- CommonSetting changed in the wrong locationApp-level 'set as default' prompts don't always update the system-wide setting.
- PossibleDesired app isn't fully installed or registered with the systemA partial install can leave an app missing from the default apps list.
- Less commonCorrupted file association settingsDeeper system settings corruption can prevent changes from sticking.
What to do
- Go to your operating system's default apps settings (Settings > Apps > Default apps on Windows, or right-click a file and choose Get Info on Mac).
- Search for the specific file type or extension and manually select your preferred app.
- On Mac, use 'Change All' after selecting the app in Get Info to apply it to all files of that type.
- Reinstall the app you want as default if it isn't appearing as an option.
- Restart the computer after changing the setting.
- Check if the app you don't want has a setting of its own that re-claims file types, and disable that if present.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.