How to unlock password for Pi account

I wanted to control my Pi with my PC via ssh. In the tutorial they recommended making a new account and locking the Pi account(for security purposes). I followed these instructions:
1.)Make New Super User/Password

sudo /usr/sbin/useradd --groups sudo -m rob

2.) Assign Password to new Super User

sudo passwd rob

3.) Uncheck the "auto login as Pi User" box in Menu->Preferences->Raspberry Pi Configuration

4.) Reboot the system

sudo reboot

5.)Ensure new user is indeed super user

sudo groups

6.) Disable the default Raspberry Pi user. Note: The reason given to do this is quote "At the time of writing the guide, the "pi" user is still needed for certain system functions. So insteed of removing it (which may cause further problems down the line), you’ll simply lock it by forcing the password to expire.)"

See code for command line entered to lock the pi account.

sudo passwd -l pi

The tutorial then informs me to update my system every now and then, which will take care of any system vulnerabilities.
They recommend entering this line into the terminal.

sudo apt-get update && sudo apt-get dist-upgrade

I got my Pi a couple of weeks ago so I’ve haven’t updated it since setup. I haven’t followed this final instruction yet.

I have two questions:

a) how do I undo this command and allow myself to log into pi@raspberry?

b) how do I easily transfer the file from one user to the other?

Edit: The file I am referring to is some python code(.py file).

Thanks

$ sudo passwd --unlock pi