Reading a binary file as text is a peculiar thing to do, but it is possible. Any of the 8-bit encodings will do it just fine. For example, the code below opens and reads an executable and outputs it to the console.
const string fname = @"C:\mystuff\program.exe";
using (var sw = new StreamReader(fname, Encoding.GetEncoding("windows-1252")))
{
var s = sw.ReadToEnd();
s = s.Replace('\x0', ' '); // replace NUL bytes with spaces
Console.WriteLine(s);
}
The result is very similar to what you'll see in Notepad or Notepad++. The "funny symbols" will differ based on how your console is configured, but you get the idea.
By the way, if you examine the string in the debugger, you're going to see something quite different. Those funny symbols are encoded as C# character escapes. For example, nul bytes (value 0) will display as \0 in the debugger, as NUL in Notepad++, and as spaces on the console or in Notepad. Newlines show up as \r in the debugger, etc.
As I said, reading a binary file as text is pretty peculiar. Unless you're just looking to see if there's human-readable data in the file, I can't imagine why you'd want to do this.
Update
I suspect the reason that all you see in the Windows Forms TextBox is "MZ" is that the Windows textbox control (which is what the TextBox ultimately uses), uses the NUL character as a string terminator, so won't display anything after the first NUL. And the first thing after the "MZ" is a NUL (shows as `\0' in the debugger). You'll have to replace the 0's in the string with spaces. I edited the code example above showing how you'd do that.
