When we create Amazon instances, we will get key as .pem file. But for logging in to the instances directly using putty, we need the private key in .ppk format.
For creating the private key in ppk, we need puttygen. Puttygen is available with the full bundle of putty. The steps are mentioned below.

1) Be ready with the private key in .pem format

2) Open the Puttygen and click on the top left option File and import the private key in .pem format.

3) Then it will be opened.

4) Choose a passphrase if required (optional)

5) Click on save private key option and save it as .ppk format.