instead of having the system defined document reference for sales , purchase documents, how to create a dynamic reference each time but the last 3 digits be the running system generated.
Please, where can i set this 
to my custom made format ( Example i want it as HR-ABZ-400) and then the next employee be added as 401 and so on.
similarly where to set such nomenclature or naming convention for other document references
Fine, i found the answer for my above quote, its here in < Settings -Data -Naming Series>
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Ok, then, the user selects the module or transaction (Example : HR), i think it displays correctly the list of transaction pertains only to the selected HR transaction type.
But coming down the “UPDATE SERIES” i think it lists the complete lots of series available in sytem. Instead it should list only the series pertain to the selected module or transaction .