get a line after a specific word from text file

Question

Hi All,

In my text file I have data like this:

[data]
123.txt
blabla

[Mobile]
345.txt
456.txt
[calls]
vsjs.txt
dsfs.txt

I would like to get these data (345.txt, 456.txt) and and the keyword to get is "[Mobile]".

I want to show  345.txt, 456.txt in rich textbox. If user makes any changes than I want  to save it back. It means If user writes 345test.txt then the text file should be like this:

[data]
123.txt
blabla

[Mobile]
345test.txt
456.txt
[calls]
vsjs.txt
dsfs.txt

Advance thanks,
Darma