Hi,
Thanks for considering Aspose.
Please consult the following example for your need:
Workbook workbook = new Workbook();
Cell cell = workbook.Worksheets[0].Cells["A1"];
cell.PutValue(3435.4376);
// Custom Currency format 1.
cell.Style.Custom = "#,##0.00$_);[Red](#,##0.00$)";
workbook.CalculateFormula();
MessageBox.Show(cell.StringValue);
cell = workbook.Worksheets[0].Cells["A2"];
cell.PutValue(3435.4376);
// Custom Currency format 2.
cell.Style.Custom = "€#,##0.00_);[Red](€#,##0.00)";
workbook.CalculateFormula();
MessageBox.Show(cell.StringValue);
cell = workbook.Worksheets[0].Cells["A3"];
cell.PutValue(3435.4376);
// Custom Decimal format 1.
cell.Style.Custom = "#,##0_);[Red](#,##0)";
workbook.CalculateFormula();
MessageBox.Show(cell.StringValue);
cell = workbook.Worksheets[0].Cells["A4"];
cell.PutValue(3435.4376);
// Custom Decimal format 4.
cell.Style.Custom = "#,##0.000_);[Red](#,##0.000)";
workbook.CalculateFormula();
MessageBox.Show(cell.StringValue);
cell = workbook.Worksheets[0].Cells["A5"];
cell.PutValue(DateTime.Now);
// Custom Date format 1.
cell.Style.Custom = "mm/dd/yy";
workbook.CalculateFormula();
MessageBox.Show(cell.StringValue);
cell = workbook.Worksheets[0].Cells["A6"];
cell.PutValue(DateTime.Now);
// Custom Date format 5.
cell.Style.Custom = "dd.mm.yy";
workbook.CalculateFormula();
MessageBox.Show(cell.StringValue);
workbook.Worksheets[0].AutoFitColumn(0);
workbook.Save("d:\\test\\testcustomformat.xls");
Thank you.