8.2.8 Saving your private key to a disk file
Once you have generated a key, set a comment field and set a passphrase, you are ready to save your private key to disk.
Press the ‘Save private key’ button. PuTTYgen will put up a dialog box asking you where to save the file. Select a directory, type in a file name, and press ‘Save’.
This file is in PuTTY's native format (*.PPK); it is the one you will need to tell PuTTY to use for authentication (see section 4.22.8) or tell Pageant to load (see section 9.2.2).