If you have the software currently installed and activated on an old machine, it will continue to work. However, if that machine fails, the software cannot be officially "moved" to a new one because a new activation code is required.
The activation generators for 2009-era software have been decommissioned. Autodesk no longer provides activation codes for perpetual licenses for these versions. autocad 2009 serial number and activation code
If you are looking to install or reactivate this legacy version, here is the official stance from Autodesk: If you have the software currently installed and
