Hi Longedge ,
For an UPGRADE the installation would uninstall the previous PDR(10) before installing PDR11.
If you purchased the FULL version, then PDR11 would install as a separate installation and the previous PDR10 would remain and be accessible.
An upgrade can be installed without a previous PDR being present, when asked for the previous activation key the install will proceed. This is for earlier versions of PDR.
Dafydd