How to Extend Known Folders with Custom Folders
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 IKnownFolderManager::GetFolderIds. Note that a known folder must be a per-machine folder. You cannot create a per-user known folder.
Define your known folder through a KNOWNFOLDER_DEFINITION structure.
Register the known folder through a call to IKnownFolderManager::RegisterFolder.
If you create a known folder for your application as part of your installation procedure, you must also include IKnownFolderManager::UnregisterFolder as part of your uninstallation code.
Give consideration to why you want your folder to be included in the known folder system before you register it. You should have a valid reason for elevating your folder to that level of system visibility.