Reading a file

I want to read data from file and convert it into string array.The file contains numbers and other characters.I want to remove the other characters and just have the numbers and then write this content into a new file.
For the above problem..Im readng the data into a byte aarray and converting it into a string array. then it will check each character in string is numeric or not .If yes then that character will be retained otherwise removed. and the data has to be written in new file.
The problem im facing in below code is ...after reading data into bytearray and converting it into string and when im displaying this string in label ..its giving three question marks in starting. (???) .Dont know y this ? mark is coming.I want to remove this question mark in starting.
MY code is given below
FileStream fs = new FileStream(Server.MapPath("a.txt"), FileMode.Open);
byte[] data = new byte[fs.Length -1];
fs.Read(data, 1, (int)fs.L ...