How can I repeat the line in notepad++?

Question

How can I repeat the line in notepad++ ?

For example I have the following input:

a 01
a 02
a 03
a 04

And I would like it to become:

Answer 1

If you have the mouse cursor on the line you want to repeat, then you can use Ctrl-D shortcut to duplicate the line. Or you can use the same shortcut selecting multiple lines.