There is no way to customize the RKM standard report, but you can create your own report to show the custom field.
as Alan's reply in this thread.
Generally the "Document" data is not truly contained in a database by default.
I use ChillKat XML ActiveX Object (it traverses the documents much easier) to pull the inidividual document fields into a .csv file then import that into database. (with MS Access, it can be completely automated)
Not only can I report, but I can manipulate the data in the database, export back to .csv the updated 'records' and perform mass updates to documents for things like category updates, review date updates, tagline verbiage changes, etc.