아래 예제가 도움이 되시길 빕니다.

string file = @"C:\Projects\EverydayProject\test.xlsx";

string connString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" +
            file + ";Extended Properties='Excel 12.0 Xml;HDR=YES;'";

OleDbConnection conn = new OleDbConnection(connString);
conn.Open();
string query = @"select * from [Table$]";

DataTable tb = new DataTable();
using(OleDbDataAdapter ad = new OleDbDataAdapter(query, conn))
{
    ad.Fill(tb);
}

conn.Close();