This string data is for custom implementations of RAD PDF which wish to associate additional information with a given PdfObject. This data is saved inside RAD PDF's storage provider and accessible both server side and client side. Because it can be accessed and changed client side (unless the document is read-only), the value of this property should be validated server side in custom implementations relying upon it.
At this time, this value is neither loaded from any PDF data opened nor saved to any output PDF documents. This behavior may change in a future release.