To authorize any connection to the AWS instance, the private key generated for the AWS account must be converted into a PuTTY key format using the associated program PuTTYgen. Open PuTTYgen from the Start menu, and click on the Conversions menu. From the drop-down tab, select Import Key.

A file dialogue will open, allowing you to select the private key downloaded from AWS. This private key will have a .pem extension:

Click Open, and the key will be imported. To generate the private key in the PuTTY format, supply an optional key phrase (a word or few words that further identify the user and which must be remembered), and click the Save Private Key button in the Actions section. Select a folder and save the key, which will now have a .ppk file extension.