Virtualization allows you to run multiple operating systems on one system. There are several popular virtual hard disk formats in use such as VDI, VMDK and VHD. Oracle VirtualBox is a free virtualization platform and supports Windows, Mac and Linux. It can boot all three major hard disk formats and has the ability to convert existing virtual hard disks to other formats using its command line tool. Virtualbox uses the VDI format by default.
Download and install the latest version of Oracle Virtualbox if it is not already installed.
Press the "Windows" key and "R" to bring up a "Run" dialog box. Type "cmd" and press "Enter" to open a command prompt.
Type "cd C:\Program Files\Oracle\VirtualBox." Change the "C" drive to the location of your "Program Files" folder.
Type "VBoxManage clonehd filename.vdi filename.vmdk --format vmdk" and press "Enter." Replace both instances of "filename" with the actual files you want to import and export. For example, you could type "VBoxManage clonehd C:\Users\Test\linux.vdi C:\Users\Test\linux.vmdk --format vmdk" if you have a VDI file named "linux.vdi" in the "C:\Users\Test" directory.
Copy your VDI file to a safe location for backup before converting it to VMDK.