Avoid Google Spreadsheet to convert an XLSX file created by Open XML SDK to XLSM

Question

I am using the Open XML SDK 2.14.0 to create Excel files. If I upload the XLSX file produced by Open XML SDK to Google Spreadsheet, it opens the file as an XLSX file but if I make any change in the spreadsheet then Google Spreadsheet changes the file type to XLSM.

The minimalistic code bellow (found in the official documentation) reproduces the issue I am having. It generate a foo.xlsx file in C:\Temp.

var filepath = @"C:\temp\foo.xlsx";

// Create a spreadsheet document by supplying the filepath.
// By default, AutoSave = true, Editable = true, and Type = xlsx.
SpreadsheetDocument spreadsheetDocument = SpreadsheetDocument.Create(filepath, SpreadsheetDocumentType.Workbook);

// Add a WorkbookPart to the document.
WorkbookPart workbookpart = spreadsheetDocument.AddWorkbookPart();
workbookpart.Workbook = new Workbook();

// Add a WorksheetPart to the WorkbookPart.
WorksheetPart worksheetPart = workbookpart.AddNewPart<WorksheetPart>();
worksheetPart.Worksheet = new Worksheet(new SheetData());

// Add Sheets to the Workbook.
Sheets sheets = spreadsheetDocument.WorkbookPart.Workbook.AppendChild<Sheets>(new Sheets());

// Append a new worksheet and associate it with the workbook.
Sheet sheet = new Sheet() { Id = spreadsheetDocument.WorkbookPart.GetIdOfPart(worksheetPart), SheetId = 1, Name = "mySheet" };
sheets.Append(sheet);

workbookpart.Workbook.Save();

// Close the document.
spreadsheetDocument.Close();

If I upload the generated file to Google Spreadsheet, it shows this is an XLSX file.

But if I change anything in the workbook then Google Spreadsheet changes the file type to XLSM.

If I generate an empty workbook from MS Excel (Office 360) I don't have this issue : Google Spreadsheet will not change the file type if I change the data.

Why does Google Spreadsheet behave like this with XLSX file generated by Open XML SDK ? What should I do to produce an XLSX file with the Open XML SDK that is not converted to XLSM by Google Spreadsheet ?

Answer 1

A nice person from the OfficeDev team found the solution : https://github.com/OfficeDev/Open-XML-SDK/issues/1093

I am posting here the solution. It seems we need to call spreadsheetDocument.AddCoreFilePropertiesPart();

Thus my code looks like :

var filepath = @"C:\temp\foo.xlsx";

// Create a spreadsheet document by supplying the filepath.
// By default, AutoSave = true, Editable = true, and Type = xlsx.
SpreadsheetDocument spreadsheetDocument = SpreadsheetDocument.Create(filepath, SpreadsheetDocumentType.Workbook);
var coreFilePropPart = spreadsheetDocument.AddCoreFilePropertiesPart();

// With DocumentFormat.OpenXml 2.14.0, AddCoreFilePropertiesPart includes an empty core.xml without a root which leads to an error when the generated file is opened in Excel
using (XmlTextWriter writer = new XmlTextWriter(coreFilePropPart.GetStream(FileMode.Create), System.Text.Encoding.UTF8))
{
  writer.WriteRaw("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n<cp:coreProperties xmlns:cp=\"https://schemas.openxmlformats.org/package/2006/metadata/core-properties\"></cp:coreProperties>");
  writer.Flush();
}

// Add a WorkbookPart to the document.
WorkbookPart workbookpart = spreadsheetDocument.AddWorkbookPart();
workbookpart.Workbook = new Workbook();

// Add a WorksheetPart to the WorkbookPart.
WorksheetPart worksheetPart = workbookpart.AddNewPart<WorksheetPart>();
worksheetPart.Worksheet = new Worksheet(new SheetData());

// Add Sheets to the Workbook.
Sheets sheets = spreadsheetDocument.WorkbookPart.Workbook.AppendChild<Sheets>(new Sheets());

// Append a new worksheet and associate it with the workbook.
Sheet sheet = new Sheet() { Id = spreadsheetDocument.WorkbookPart.GetIdOfPart(worksheetPart), SheetId = 1, Name = "mySheet" };
sheets.Append(sheet);

workbookpart.Workbook.Save();

// Close the document.
spreadsheetDocument.Close();

And thus Google sheets stop changing from XLSX to XLSM !