This post explains how to convert ppk key to pem on Mac.
Let’s install putty using brew.
brew install putty
Execute the following command to convert ppk to pem.
puttygen key.ppk -O private-openssh -o key.pem
where,
key.ppk is your ppk file
key.pem is new name of your key file.
Change the permission of the newly created pem.
chmod 600 key.pem
Note that, the above command should be executed where ppk exist.