Convert pem to ppk file Using PuTTygen
Convert PEM files to PPK format for secure SSH access using PuTTYgen.
When you create an EC2 instance, aws provides you with .pem file. This .pem file is used to connect EC2 instance from a Linux host. In case you want to connect to EC2 instance via PuTTY, you need to convert .pem to .ppk.
Download PuTTY Key Generator , you must download puttygen.exe software and open it

Choose Load. By default, PuTTYgen displays only files with the .ppk extension. To locate your .pem file, select the option to display All Files

Once you load the .pem file, click on OK for successfully import notice

Click on Save Private Key, give a name to your key file and make sure the extension is .ppk
Now Open PuTTY, give aws public ip address. Navigate to Connection >> SSH >> Auth

Browse to navigate the .ppk file and click on Open

Choose Open again, and then choose Yes to trust this connection in the future

Log in using default user names ec2-user

Enjoy!