Selecting the "Document Author" rename option uses the document author metadata embedded in the PDF file in the renamed file name.

 

Some documents do not have the "Document Author" metadata set in the PDF.  If the "Document Author" metadata is empty, a "-" character is substituted in the renamed file.

 

You can view the PDF metadata fields by opening the PDF in Adobe Acrobat Reader DC and viewing the "Document Properties" under the "File" menu.