CellRange usedCellRange = worksheet.UsedCellRange;

            for (int row = 0; row < usedCellRange.RowCount; row++)
            {
                for (int column = 0; column < usedCellRange.ColumnCount; column++)
                {
                    ICellValue cellValue = worksheet.Cells[row, column].GetValue().Value;
                    if (cellValue.ValueType == CellValueType.Formula)
                    {
                        worksheet.Cells[row, column].SetValue(cellValue);
                    }
                }
            }