Load excel file from resources/assembly in C#

You need to extract the resource (in this case an excel spreadsheet) from the assembly and write it as a stream to a File, eg:

Assembly asm = Assembly.GetExecutingAssembly();
string file = string.Format("{0}.UTReportTemplate.xls", asm.GetName().Name);
Stream fileStream = asm.GetManifestResourceStream(file);
SaveStreamToFile(@"c:\Temp\Temp.xls",fileStream);  //<--here is where to save to disk
Excel.Application xlApp = new Excel.Application();
xlWorkBook = xlApp.Workbooks.Open(@"c:\Temp\Temp.xls");
if (xlWorkBook  == null)
{
   MessageBox.Show("Error: Unable to open Excel file.");
   return;
}
//xlApp.Visible = false;

...

public void SaveStreamToFile(string fileFullPath, Stream stream)
{
    if (stream.Length == 0) return;

    // Create a FileStream object to write a stream to a file
    using (FileStream fileStream = System.IO.File.Create(fileFullPath, (int)stream.Length))
    {
        // Fill the bytes[] array with the stream data
        byte[] bytesInStream = new byte[stream.Length];
        stream.Read(bytesInStream, 0, (int)bytesInStream.Length);

        // Use FileStream object to write to the specified file
        fileStream.Write(bytesInStream, 0, bytesInStream.Length);
     }
}