Why I can't copy cells in a notebook

Questions
1

I try to copy cells in my notebook to re-arrange topics. But I can’t do that. How I can solve this problem?

2

You certainly can. You can select cells by clicking on the blue bracket on the right. You can also select groups. And you can use Shift- as you would in any other context. You can use Option-

3

Thank you. I proceed as per your advice. But no luck. Note that in Option Inspectors, when I go to Cell Duplicates, its false and I can 't turn it to true.

4

Do you have a full license? Are you using CDF player? Are you able to add new cells? I’m not aware of any option called CellDuplicates. There is CellEditDuplicates and other similar, but they don’t have anything to do with being able to edit notebooks.