I wanted to offer a follow up to this. I know it's been a little bit (about 9 months).
First, I've only ever had to concern myself with .ppk files when using PuTTY on Windows. I live in a UNIX world.
You can indeed install PuTTY on a UNIX box, but you won't need to use .ppk files - PEM is standard - like everywhere else (besides Windows)
On Wndows, you know longer need a 3rd party client such as PuTTY. You can check your system here and make sure you're good to go. Basically, anything after Windows 10, build 1809, and Powershell version 5.1 or later. You can follow this guide to make sure you're good to go:
https://learn.microsoft.com/en-us/windows-server/administration/openssh/openssh_install_firstuse?tabs=guiNow, we all have our favorite tools, and once upon a time in Windowsland PuTTY was kewl. Actually, PuTTY was never kewl, although there is a fork where your list of remotes is stored in a file for portability instead of in the registry. So, the list of remote systems in a picker list where you can just double click to launch your SSH or other sessions is a good thing. PuTTY is highly configurable, and that's a good thing too, but in a rare departure from advising people to use FOSS instead of a proprietary solution, I've found that I prefer the community edition of MobaXTerm instead.
https://mobaxterm.mobatek.net/ - The community edition allows for 12 saved sessions, and will even import existing saved sessions from PuTTY. And best of all, you don't need to concern yourself with converting PEM to .ppk because it supports standard PEM.
If you want to convert between PEM and a .ppk, here's the basics:
$ puttygen sshkey.ppk -O private-openssh -o sshkey.pem
or
$ puttygen sshkey.pem -o sshkey.ppk -O private
In Powershell Here's the instructions, from our own Wiki, for creating your Ed25519 key pair here:
https://tilde.team/wiki/ssh#windows-10I hope that helps!