Windows bulk renaming/replace the string

I'm trying to rename the file from one format to other format.. 500+ files. Currently with notepad++ manually do it with individual file name.
Is there any command or scripts is there, Please let me know, much appreciate all your help on this.

DB2.V12.RPT(DDG1RP01)
DB2.V12.RPT(DDG1RP02)
DB2.V12.RPT(DDG1RP03)
DB2.V12.RPT(DDG1RP04)

want to rename into

ren DB2.V12.RPT(DDG1RP01)      DDG1RP01.txt
ren DB2.V12.RPT(DDG1RP02)      DDG1RP02.txt
ren DB2.V12.RPT(DDG1RP03)      DDG1RP03.txt
ren DB2.V12.RPT(DDG1RP04)      DDG1RP04.txt

that is, remove these "DB2.V12.RPT(" and ")' and rename into .txt file.