To install Windows 8 to 11 or their server versions, you have 2 options :

• use the installation DVD if you bought it in a store
• or create a bootable USB key from the iso file downloaded from the Microsoft site (or one of its resellers, such as Digital River, for example)

In this tutorial, we will create a Windows 8.1 bootable USB key, but the software we will be using will work with Windows 7, 8, 8.1, 10, 11 and their server versions (2008 R2, 2012, 2012 R2 and 2016).
To begin, download the "Windows USB/DVD Download Tool" software from the Microsoft website.

Important : this tool is no longer available on Microsoft servers.
All official download links for this tool are dead.
If you still want to use it, you'll need to download it from a third-party site, like FileHippo for example.

When you attempt to install it, a warning will appear regarding .Net Framework 2.0.

However, on Windows 8 / 8.1, you will have to enable the corresponding feature and not download the .Net Framework 2.0 from the Microsoft site to install it.

To do this, go to the control panel -> Programs -> Programs and Features.
Then, click on "Turn Windows features on or off" in the left menu.

Check the ".NET Framework 3.5 (includes .NET 2.0 and 3.0)" box and click OK.

Click "Download files from Windows Update".

Once the .NET Framework 2.0 is installed, restart the installation of "Windows USB/DVD Download Tool" and click on Next.

Once this program is installed, launch it and click on Browse.
Choose the iso file of Windows 8.1 (or any other version of Windows supported by this program) and click on Next.

Click on "USB Device".

Choose your USB key from the list.

Warning, as indicated in this warning, all the data present on this one will be deleted.
Click "Erase USB Device".

Confirm the deletion of the files from your USB key by clicking Yes.

The program will format your USB key.

Then, copy the files contained in the iso file to your USB key.

Once the bootable USB key has been created, the message "Backup complete" will be displayed.

As you can see, your USB key has the same icon as a Windows installation DVD.

The contents of your USB key are identical to the contents of the Windows installation DVD.