How to connect to a remote server using putty generated key

I'm trying to connect to a remote server using Remote Explorer extension in VSCode but when I use putty generate private key private.ppk I get an error

Could not establish a connection to

When I read through the error log, at the point it tried to load key "C:\Users\user.ssh\private.ppk" It says Invalid Format

How can I use putty format key to connect? Below is how my config looks like

Host ###.##.##.###
  HostName ###.##.##.###
  User <user>
  Port 22
  IdentityFile C:\Users\user\.ssh\private.ppk