When the VM uses a Linux or Unix OS, in case you need to access the ISO from the OS, you will need to issue a manual mount command before a virtual CD drive can be connected and made available for use.
The command will vary, depending on the OS type.
The following is a manual command example for Ubuntu:
mount /dev/cdrom /media/cdrom
The following is a manual command example for Unix:
cfgmgr -l vscsi0 lsdev -Cc cdrom
crfs -v cdrfs -p ro -d cd0 -m /cdrom -An mount /cdrom
In both of these scenarios, in order to use the CD after mounting, you will also need to change to the relevant CD-ROM directory.