SSH file conversion details are described here.
Convert you SSH .pem file to .ppk file.
For this you need to have the puTTY genputty key gen application installed in your machine. Download putty here.
If the above link doesn’t work use this link. click Download putty, on the landing page, you download and install the puTTygen.exe or all binary packages in zip format. I recommend to download and install all, this will used later, when you login using keys.
Once you installed puTTygen, open it and either click Load button in the Actions section or select Import key from Conversions menu item. Highlighted in the below Figure 1.
Important things to be noted : Select SSH-2 RSAKey Type type of key to be generate in parameter.
If you have chosen the LoadLoad option in the Figure 1 option to load the key, you have to choose the file format to all file to load the .pem file, see Figure 2.
Load SSH pem key
Once the key is loaded, next save the key by using Save private key button. Enter the name you want and save it. Figure 3.
Save PPK file
That’s it, you have converted SSH .pem file to .ppk file.