Notes about the VDMK file extension:
To open this file type, a required software must be installed. Without it you only see a Windows message "The following file cannot be opened
" (Windows 7) or "How do you want to open this file?
" (Windows 10) if you double-click the file. There click on "More apps"
and choose a suitable software to view such files on your PC or from email attachments.
The VDMK file type is primarily associated with 'VMware' by VMware, Inc.. It's possible this is a misnamed VMDK file which is the usual file extension for VMware Virtual Disks. However, there are a number of entries in a Google search that refer to this specific file extension for that purpose.