In C# it is quite convenient to read all files to an array. You can use the method ReadAllLines() from the File class, all it needs is a path to the file that you want to read. This does just what you are looking for, here is an example:
var lines = File.ReadAllLines("C:\\someTextFile.txt");
Using the above you will have an array containing each line of the file as a string, you can then call
ToList(); to get it as a list.
I hope this helps you :)