a) make an zero-width selection in front of the lines
b) execute "Edit > Advanced > Numbering..."
c) press [OK]
Note: to pad with zeros enter them into the "First Line" field like "01" or "0001"

d) while still have that inserted numbers selected do an regex s&r:
Find: (\d\d)
Replace with: \1)

[X]Use regex
[X]In selection only

Note: the amount of find "\d" patterns depends on how many zeros you have padded.
"\d\d" will match two digits.
"\d\d\d" or "\d{3}" will match three, and so on...

You can use Insert Sequence Numbers plug-in (32-bit)

or a .jsee-macro like this one:

var n = document.GetLines();
var a = new Array();
for (var i=1; i<(n+1); i++) a.push(i + ") " + document.GetLine(i));
document.selection.SelectAll();
document.write(a.join("\n"));
Quit();

hello!

I want to number the lines of a text file, by inserting 1), 2), 3), etc at the begining of each line

how can this be done?

thanks!