Any documentation for PDDocExportUserProperties?

I was looking through the Acrobat SDK Plugin Guide and saw the section of "Exporting data from PDF document objects".  The section mentions using the "PDDocExportUserProperties" method to retrieve data from a PDF document object. I'm curious as to what kind of user properties are gotten from this method, but I can't find anything about this method other than the page that references the method. What does this method return if anything?  Is there an alternative way to getting this PDF document object data?  

Here is the link to the "Exporting data from PDF document objects"  section.

https://help.adobe.com/pdfl_sdk/18/PDFL_SDK_HTMLHelp/PDFL_SDK_HTMLHelp/index.html#t=PDFL_MasterBook%2FUnderstanding_Plug-ins%2FExporting_data_from_PDF_document_objects.htm