[c#] Reliable way to convert a file to a byte[]

Others have noted that you can use the built-in File.ReadAllBytes. The built-in method is fine, but it's worth noting that the code you post above is fragile for two reasons:

  1. Stream is IDisposable - you should place the FileStream fs = new FileStream(filename, FileMode.Open,FileAccess.Read) initialization in a using clause to ensure the file is closed. Failure to do this may mean that the stream remains open if a failure occurs, which will mean the file remains locked - and that can cause other problems later on.
  2. fs.Read may read fewer bytes than you request. In general, the .Read method of a Stream instance will read at least one byte, but not necessarily all bytes you ask for. You'll need to write a loop that retries reading until all bytes are read. This page explains this in more detail.