How to search a keyword in multiple files? and copy them to other files using C#

I'm stuck on how i gonna search a certain keyword in Multiple text file and want to copy them to new text files...Furthermore, if the keyword that i want to search is found (maybe in a file contain one or more keyword that i want to search), i want to copy 2 line above and 2 line below the keyword.

So, at the new file should contain from which file it copy from, the whole line of the keyword +2line above and below the keyword.

Please help me out,im a newbies in the programming world but been ask to do very challenging task. If my problem does not clear, please let me know.

Thanks in advance...