Depends on the 'type' of drive it is?
Standard 'old' type of MBR drive or the newer GPT disk format used with uEFI BIOS.
Standard limits you to up to 4 PRIMARY PARTITIONS. However, if you create a LOGICAL PARTITION you can create more logical drives letters within it.
GPT drives have no such limits but the OS can impose some, like C: to Z: only allowed.
Suspect your hard drive might have 4 partitions already, the vendor may have created them, one for the OS (C
, another for re-install (D:, could be hidden from the OS), a diagnostic partition, and the boot partition record. Open up Disk Manager can look to see how many you have? If you have 4 primary there isn't much other than deleting one or using the space as an addition to an existing drive.