Check out example codes for "merge xml files into one c#". It will help you in understanding the concepts better.

Code Example 1

using (var output = File.Create(originalFileName))
{
  foreach (var file in new[] { "File1", "File2" })
  {
    using (var input = File.OpenRead(file))
    {
      input.CopyTo(output);
    }
  }
}

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