vEOS is free for lab use but will drop to a limited feature set (2 VRF, 4 VLANs per interface) after 60 days without a license. A "Developer" or "Test" license can be obtained from Arista.
In essence, veos-4.27.0f.vmdk is a pre-configured, bootable virtual hard disk that runs a full-featured Arista switch operating system. veos-4.27.0f.vmdk
If you have a standalone .vmdk but no OVF, you can create a new VM: vEOS is free for lab use but will