From putty documentation
5.2.2.6 -pw passw login with specified password
If a password is required to connect to the host, PSCP will interactively prompt you for it. However, this may not always be appropriate. If you are running PSCP as part of some automated job, it will not be possible to enter a password by hand. The -pw option to PSCP lets you specify the password to use on the command line.