The Userproperties metadata can be found in PDF files. It’s information that can be set by the user, or rather creator, of a PDF document. It is usually used to provide additional information about the creator or company that produced the document, business that uses or distributes the PDF, or other information that could not be given using the already present meta information such as company, creator, etc.
In order for a PDF to contain these Userproperties, they have to be defined as a namespace within the metadata of a PDF document first. Then, the value can be added. However, when checking a file for hidden data, the Userproperties only gives an indication if such a namespace is present in the file (“yes”) or not (“no”), not the actual set Userproperties.
Userproperties are also known as “XMP User Properties”.