The qemu-img command is pre-installed on Proxmox, and can be used to convert (with the convert option) the "disk image filename" to another disk image format.


And here's most used format supported by the convert arg

Image format Argument
QCOW2 (KVM, Xen) qcow2
VMDK (VMware) vmdk
VHD (Hyper-V) vhd
raw raw
VDI (VirtualBox) vdi
QED (KVM) qed

We have a VMDK used in VMware product (ESXI for exemple), we can convert it to qcow2

qemu-img convert -f vmdk openmanage_enterprise.x86_64-0.0.1-disk1.vmdk -O qcow2 OpenManageEntreprise-3-1.qcow2

Result of the command