Convert an Epplus ExcelPackage to a CSV file, returning the byte[] array of this new CSV file. Taking the code provided by "Brad" at http://codejournal.blogspot.co.uk/2012/03/using-epplus-library-to-convert-xlsx-to.html and creating an extension method from it which can be called on Epplus' ExcelPackage. Just call excelPackageObject.ConvertToCsv();

gistfile1.txt

using OfficeOpenXml;
using System.Collections.Generic;
using System.IO;
using System.Text;

namespace WebUI.Infrastructure
{
    public static class StringUtils
    {
        private static string DuplicateTicksForSql(this string s)
        {
            return s.Replace("'", "''");
        }

        /// <summary>
        /// Takes a List collection of string and returns a delimited string.  Note that it's easy to create a huge list that won't turn into a huge string because
        /// the string needs contiguous memory.
        /// </summary>
        /// <param name="list">The input List collection of string objects</param>
        /// <param name="qualifier">
        /// The default delimiter. Using a colon in case the List of string are file names,
        /// since it is an illegal file name character on Windows machines and therefore should not be in the file name anywhere.
        /// </param>
        /// <param name="insertSpaces">Whether to insert a space after each separator</param>
        /// <returns>A delimited string</returns>
        /// <remarks>This was implemented pre-linq</remarks>
        public static string ToDelimitedString(this List<string> list, string delimiter = ":", bool insertSpaces = false, string qualifier = "", bool duplicateTicksForSQL = false)
        {
            var result = new StringBuilder();
            for (int i = 0; i < list.Count; i++)
            {
                string initialStr = duplicateTicksForSQL ? list[i].DuplicateTicksForSql() : list[i];
                result.Append((qualifier == string.Empty) ? initialStr : string.Format("{1}{0}{1}", initialStr, qualifier));
                if (i < list.Count - 1)
                {
                    result.Append(delimiter);
                    if (insertSpaces)
                    {
                        result.Append(' ');
                    }
                }
            }
            return result.ToString();
        }
    }

    public static class EpplusCsvConverter
    {
        public static byte[] ConvertToCsv(this ExcelPackage package)
        {
            var worksheet = package.Workbook.Worksheets[1];

            var maxColumnNumber = worksheet.Dimension.End.Column;
            var currentRow = new List<string>(maxColumnNumber);
            var totalRowCount = worksheet.Dimension.End.Row;
            var currentRowNum = 1;

            var memory = new MemoryStream();

            using (var writer = new StreamWriter(memory, Encoding.ASCII))
            {
                while (currentRowNum <= totalRowCount)
                {
                    BuildRow(worksheet, currentRow, currentRowNum, maxColumnNumber);
                    WriteRecordToFile(currentRow, writer, currentRowNum, totalRowCount);
                    currentRow.Clear();
                    currentRowNum++;
                }
            }

            return memory.ToArray();
        }

        /// <summary>
        /// 
        /// </summary>
        /// <param name="record">List of cell values</param>
        /// <param name="sw">Open Writer to file</param>
        /// <param name="rowNumber">Current row num</param>
        /// <param name="totalRowCount"></param>
        /// <remarks>Avoiding writing final empty line so bulk import processes can work.</remarks>
        private static void WriteRecordToFile(List<string> record, StreamWriter sw, int rowNumber, int totalRowCount)
        {
            var commaDelimitedRecord = record.ToDelimitedString(",");

            if (rowNumber == totalRowCount)
            {
                sw.Write(commaDelimitedRecord);
            }
            else
            {
                sw.WriteLine(commaDelimitedRecord);
            }
        }

        private static void BuildRow(ExcelWorksheet worksheet, List<string> currentRow, int currentRowNum, int maxColumnNumber)
        {
            for (int i = 1; i <= maxColumnNumber; i++)
            {
                var cell = worksheet.Cells[currentRowNum, i];
                if (cell == null)
                {
                    // add a cell value for empty cells to keep data aligned.
                    AddCellValue(string.Empty, currentRow);
                }
                else
                {
                    AddCellValue(GetCellText(cell), currentRow);
                }
            }
        }

        /// <summary>
        /// Can't use .Text: http://epplus.codeplex.com/discussions/349696
        /// </summary>
        /// <param name="cell"></param>
        /// <returns></returns>
        private static string GetCellText(ExcelRangeBase cell)
        {
            return cell.Value == null ? string.Empty : cell.Value.ToString();
        }

        private static void AddCellValue(string s, List<string> record)
        {
            record.Add(string.Format("{0}{1}{0}", '"', s));
        }
    }
}

Thank you. Exactly what I needed

me too

worksheet position out of range error is occuring

@nitinjs, you can give the sheet name as
var worksheet = package.Workbook.Worksheets[sheet_name];

This error occurs because there's no sheet with the index 1 in the ExcelPackage. This means only one sheet is there, which has index 0.
So either give 0 or the sheet name, if any.

Excellent!!!!!

I tried the above solution, but after returning the bytes to client side, and then downloading the files, its converting Japanese Characters to ??
Any solution

@pankajitengg I'm guessing here but might need to replace Encoding.ASCII with something else; Encoding.UTF8 or Encoding.UTF16 perhaps?

@pankajitengg I'm guessing here but might need to replace Encoding.ASCII with something else; Encoding.UTF8 or Encoding.UTF16 perhaps?

Thanks.. It worked with Encoding.UTF8...