http://docs.notepad-plus-plus.org/index.php/Inserting_Variable_Text
Notepad++ comes equipped with a Edit -> Column "Alt+C" Editor which can work on a rectangular selection in two different ways: Coledit.png inserting some fixed text on every line including and following the current line, at the column of the insertion point (aka caret). Initially selected text is left untouched. As the picture illustrates, a linear series of numbers can be inserted in the same manner. The starting value and increment are to be provided. Left padding with zeroes is an option, and the number may be entered in base 2, 8, 10 or 16 - this is how the computed values will be displayed too, padding being based on the largest.