File Associations

File associations are managed in the HKEY_CLASSES_ROOT hive of the registry.


In HKEY_CLASSES_ROOT, there is one key per file extension.

Each key has a default value corresponding to the file type.

For example, let’s looking at the .docx file extension.


Here the default value for .docx is Word.Document.12



In HKEY_CLASSES_ROOT, there is also one key per file type.

All these keys have the following sub-keys:

  • Shell
    • Open
      • Command

The default value of the sub-key “command” defines the command run when the file is launched.