C#

DataSet ds = new DataSet();
            //Provider String Extended properties: 
            //"Excel 12.0": Use Excel (xls or xlsx) as source
            //"Header Yes": Header is included in the Excel sheet
            //"IMEX=1": When reading from the excel sheet ignore datatypes and read all data in the sheet.
            //Without setting IMEX=0, the excel reader looks for the datatype in the excel sheet.
            //The code below in comments was used for reading xls file
            //OleDbConnection con = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + FileName + ";Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=1\"");
            // The code below is the one i am using for reading an xlsx file
            OleDbConnection con = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + FileName + ";Extended Properties=\"Excel 12.0;HDR=YES;IMEX=1;MAXSCANROWS=0\"");
            con.Open();
            try
            {
                //Create Dataset and fill with imformation from the Excel Spreadsheet for easier reference
                DataTable dt = con.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);
                string sheetname = dt.Rows[0]["TABLE_NAME"].ToString();

                OleDbDataAdapter myCommand = new OleDbDataAdapter(" SELECT * FROM [" + sheetname + "]", con);
                myCommand.Fill(ds);
                
            }
            catch (Exception ex)
            {
                string exce = ex.Message;
            }
            finally
            {
                con.Close();
            }
            return ds;