Windows 10’s file association protection mechanism prevents direct changes to the UserChoice area of the registry for each file type. When no file association (user choice) is set in the registry or if an application makes the hash void by incorrectly writing to UserChoice registry key to set associations, this triggers a reset of file association for that file type, going back to Windows 10 defaults.
For instance, Edge may takeover your PDF file associations after an update, or due to the above-mentioned reasons, and the Action Center notifies you that an app default was reset.
“An app caused a problem with the default app setting for .pdf files, so it was reset to Microsoft Edge”
2019 Update: The following registry edits no longer work in Windows v1809 (and higher). See the article Fix “An App Default Was Reset” for a proper fix.
Solution
Use the following steps to stop Microsoft Edge from hijacking the PDF, or .HTM/.HTML file associations.
The instructions work in builds older than v1803.
1. Start the Registry Editor (Regedit.exe) and go to:
HKEY_CURRENT_USER\SOFTWARE\Classes\Local Settings\Software\Microsoft\Windows\CurrentVersion\AppModel\Repository\Packages\Microsoft.MicrosoftEdge_25.10586.0.0_neutral__8wekyb3d8bbwe\MicrosoftEdge\Capabilities\FileAssociations
Note: The above key applies if you have Microsoft Edge v25.10586.0.0 installed, which is the current version as of this post. If you have any other build number, choose the appropriate key. It will be usually in this format:
Microsoft.MicrosoftEdge_nn.nnnnn.n.n_neutral__8wekyb3d8bbwe, Where the nnn… is a placeholder for the actual version/build no.
2. In the right-pane, note down the Prog IDs assigned for .pdf, and .htm or .html file types. In this case, the Prog ID for .pdf is AppXd4nrz8ff68srnhf9t5a8sbjyar1cr723
3. Go to the following location
HKEY_CURRENT_USER\SOFTWARE\Classes\AppXd4nrz8ff68srnhf9t5a8sbjyar1cr723
In the right-pane, create a string value (REG_SZ) named NoOpenWith
This prevents the .PDF file association takeover by Microsoft Edge. The NoOpenWith entry works on a per-ProgID basis. For .HTM/.HTML files, add the NoOpenWith entry here:
HKEY_CURRENT_USER\SOFTWARE\Classes\AppX4hxtad77fbk3jkkeerkrm0ze94wjf3s9
Anniversary Update: If you’re using Windows 10 Anniversary Update, you also need to create an additional string value named NoStaticDefaultVerb in the above key.
4. Exit the Registry Editor.
5. Use Default Programs to re-associate the file type with your preferred program.
Note that this registry edit also hides Microsoft Edge in the Open With dialogs for the corresponding file types.
Important: On Windows 11, the NoOpenWith registry value behaves differently and causes issues. For more information, check out the article Can’t Associate JPG/PNG Files via Default Apps in Windows 11