Independent software vendors (ISVs) can extend the set of known folders on a system by registering known folders of their own. Once registered, those third-party folders are known to the system. They are found by any call to GetFolderIds. Note that a known folder must be a per-machine folder. You cannot create a per-user known folder.

It is a simple matter to register a new known folder.

1. Define your known folder through a KNOWNFOLDER_DEFINITION structure.
2. Register the known folder through a call to RegisterFolder.

If you create a known folder for your application as part of your installation procedure, you must also include UnregisterFolder as part of your uninstallation code.

Give consideration to why you want your folder to be included the known folder system before you register it. You should have a valid reason for elevating your folder to that level of system visibility.