How can connect server using .ppk key file
Solution 1:
You can use PuTTY in Ubuntu as well
sudo apt-get install putty
The equivalent to Putty in Linux, however, is to use ssh on the command line
ssh -i ~/.ssh/key user@server
You will need to convert your putty key (using PuTTYgen) to an openssh key or make a new key.
To convert the key, first import it, then export it as an openssh key.
See: https://help.ubuntu.com/community/SSH/OpenSSH/ConnectingTo
You can use any number of programs to connect similar to WinSCP, nautilus will do it
Key-based SSH login with Nautilus' "Connect to Server"
You can also use gftp