It can happen automatically. Rapture Session looks for Rapture during installation. If Rapture is detected, the Rapture Session installer copies the programs from "C:\ProgramData\Cakewalk\Rapture\Programs" into its program library "C:\Cakewalk Content\Rapture Pro\Programs\Rapture (legacy)" and sets "Rap Multisample Path" in
HKEY_LOCAL_MACHINE\SOFTWARE\Cakewalk Music Software\Rapture Session\2.0. It performs similar activities for DPro and Cakewalk Sound Center.
While it is possible to perform these activities manually. The easiest way may be to rerun the Rapture Session installer.