File Handler behavior in managed code

In native COBOL if you have "SELECT DATA-FILE ASSIGN TO DISK 'OLD\Data.dat'" and "OPEN INPUT DATA-FILE" then the File Handler will look for an environment variable named "dd_OLD" and replace the "OLD" in the SELECT clause literal with the contents of the environment variable (if found). But what happens in managed code? We are getting "File not found". Is the managed-code version of the File Handler looking for "dd_OLD" somewhere other than in the environment, or does this functionality not exist in managed code?