System.Text.Encoding enc = null;
System.IO.FileStream file = new System.IO.FileStream(filePath,
    FileMode.Open, FileAccess.Read, FileShare.Read);
if (file.CanSeek)
{
    byte[] bom = new byte[4]; // Get the byte-order mark, if there is one
    file.Read(bom, 0, 4);
    if ((bom[0] == 0xef && bom[1] == 0xbb && bom[2] == 0xbf) || // utf-8
        (bom[0] == 0xff && bom[1] == 0xfe) || // ucs-2le, ucs-4le, and ucs-16le
        (bom[0] == 0xfe && bom[1] == 0xff) || // utf-16 and ucs-2
        (bom[0] == 0 && bom[1] == 0 && bom[2] == 0xfe && bom[3] == 0xff)) // ucs-4
    {
        enc = System.Text.Encoding.Unicode;
    }
    else
    {
        enc = System.Text.Encoding.ASCII;
    }
 
    // Now reposition the file cursor back to the start of the file
    file.Seek(0, System.IO.SeekOrigin.Begin);
}
else
{
    // The file cannot be randomly accessed, so you need to decide what to set the default to
    // based on the data provided. If you're expecting data from a lot of older applications,
    // default your encoding to Encoding.ASCII. If you're expecting data from a lot of newer
    // applications, default your encoding to Encoding.Unicode. Also, since binary files are
    // single byte-based, so you will want to use Encoding.ASCII, even though you'll probably
    // never need to use the encoding then since the Encoding classes are really meant to get
    // strings from the byte array that is the file.
 
    enc = System.Text.Encoding.ASCII;
}
 
// Do your file operations here, such as getting a string from the byte array that is the file
byte[] buffer = new byte[4096]; // A good buffer size; should always be base2 in case of Unicode
while (file.Read(buffer, 0, 4096))
{
    string line = enc.GetString(buffer); // Uses the encoding we defined above
    System.Console.Write(string);
}
System.Console.WriteLine();
 
// Close the file: never forget this step!
file.Close();

 
System.IO.FileStream file = null;
try
{
    // Please all the code from above in here, except we define "file" outside the try-catch-finally block
    // since the "finally" block will need to have "file" defined and defining in the "try" block will be in a
    // different scope.
}
catch (Exception e)
{
    Console.Error.WriteLine("Error: " + e.Message);
}
finally
{
    // Make sure we don't throw a NullReferenceException since the "file" object may not have been
    // instantiated yet, perhaps because of an exception throw when you declare a new FileStream.
    if (file != null)
        file.Close();
}