You can use your bow during rifle season, but you must wear hunters' orange. You do not need a bow stamp. Click here for more information. But you can use one during rifle season. It cannot be used to finish off an arrow-wounded animal.
Field dress the animal to keep it from spoiling.
Leave it where it was killed, preferably with a person watching it. Report what happened and wait for instructions from a game warden. There have been no confirmed cases of CWD in the wild in Montana and there is no evidence that the disease is transmissible to humans. However, if you are concerned wear protective gloves while field-dressing game. Minimize handling and don't eat the brain or spinal cord.