Load excel workbook from memory stream.

// Get content of your Excel file
var ms = new MemoryStream(...);

// Get temp file name
var temp = Path.GetTempPath(); // Get %TEMP% path
var file = Path.GetFileNameWithoutExtension(Path.GetRandomFileName()); // Get random file name without extension
var path = Path.Combine(temp, file + ".xlsx"); // Get random file path

using (var fs = new FileStream(path, FileMode.Create, FileAccess.Write))
{
    // Write content of your memory stream into file stream
    ms.WriteTo(fs);
}

// Create Excel app
Excel.Application excel = new Excel.Application();

// Open Workbook
excel.Workbooks.Open(path, ReadOnly: true);

Path.GetTempPath()

Path.GetFileNameWithoutExtension(Path.GetRandomFileName())

TempFileCollection()

System.CodeDom.Compiler

using (var tempfile = new TempFileCollection())
{
    string filePath = tempfile.AddExtension("temp"); // or whatever you want to use
    using (FileStream fs = new FileStream(filePath, FileMode.OpenOrCreate))
    {
        fs.Write(YourByteArray, 0, YourByteArray.Length);
    }
    // Here is your code of what you want to do with this file, fill it, print it, or whatever
}
// Here the file is deleted automatically