create a new layer, and select the text tool
then make sure you have selected dynamic text. on the drop
down menu left bottom
now draw a text area where like how your text area should
look like and type some text on it and press enter after finishes
now what you have to do is on the right of the stage you will
find a panel named "Components" from there you will
Then drag "scrollBar" to the stage
and drop it inside right in the text box. Then it will look
like the way shown below in the image. Now you can type more
text as you want on the text box......NO worries how ever
much you typed on the text box its added to the scroll bar.....
Press Ctrl+enter and see how it works......
It should work very well.......