How to convert the ppk files to openssh format
How to convert putty generated .ppk files to .pem/openssh format
2. Choose the .ppk file, and then choose Open.
3. Choose Conversions from the menu at the top of the PuTTY Key Generator, and then choose Export OpenSSH Key.
4. For the PuTTYgen warning Are you sure you want to save this key without a passphrase to protect it?, choose Yes.
5. Name the file and add the .pem extension.