While third-party sites may offer Windows 8.1 VHD download links, it's crucial to prioritize security and consider the benefits of using official channels or newer, supported operating systems. Always ensure that any software download is from a trusted source to protect your data and computer.

If you have an ISO, you can follow these general steps to create your own bootable VHD file: Restore .vhdx/.vhd system image - Microsoft Q&A

Finding an official has become difficult since Microsoft ended support for the operating system in January 2023. Previously, Microsoft offered pre-configured virtual machines (VMs) for developers, but these official repositories have largely been removed.

To make the VHD bootable, you must apply the Windows image from your ISO to the virtual disk: Double-click your downloaded ISO file.