Even when you use the ProcessStartInfo Class, if you have to add spaces for arguments, then the above answers won’t solve the problem. There’s a simple solution. Just add quotes around arguments. That’s all.
string fileName = @"D:\Company Accounts\Auditing Sep-2014 Reports.xlsx";
System.Diagnostics.ProcessStartInfo startInfo = new System.Diagnostics.ProcessStartInfo();
startInfo.FileName = "Excel.exe";
startInfo.Arguments = "\"" + fileName + "\"";
System.Diagnostics.Process.Start(startInfo);
Here I’ve added escaped quotes around filename, and it works.