This page contains download links for the latest released version of PuTTY. Currently this is 0.70, released on 2017-07-08. When new releases come out, this page will update to contain the latest, so this is a good page to bookmark or link to.
No, putty is analagous to ssh and pscp to scp. PuTTY provides the overall functionality as does SSH. However, ssh and putty (non-capitalized) are interactive (as well as non-interactive by supplying shell commands as arguments) command line interfaces within the greater context of what PuTTY and SSH can do. Scp and pscp are secure versions of the ftp Linux/Unix command (with similar, but not identical, command sets) which use the SSH protocol to securely authenticate and transfer files.
So essentially, there is not a way to combine them. The Unix philosophy is that one tool does one thing and does it really well. Possibly plink could be used for many things (it is a backend to PuTTY functionality).
But even if possible, it would take much more code to copy files with any sort of backend interface like pscp than using the pscp command which reduces the very complex process of copying files to a simple source and destination. I realize that you are trying to avoid making a separate connection to the server, but as far as I know, even if you did use pscp, there would still need to be a separate connection to transfer the file's contents because the first connection is connected to a remote shell.
– Feb 17 '14 at 3:41.