Creating an excel file with EPPlus, but it is always read-only

Question

I'm creating/sending a file with EPPlus like this:

using (ExcelPackage package = new ExcelPackage())
{

    ExcelWorksheet worksheet = package.Workbook.Worksheets.Add("Sheet");
    ... //create file here

    Response.Clear();
    Response.ContentType = "application/xlsx";
    Response.AddHeader("content-disposition", "attachment; filename=" + filename + ".xlsx");
    Response.BinaryWrite(package.GetAsByteArray());
    Response.End();
}

Everything works fine, except the file always comes back as read-only, and I can't figure out why. Within the "package" object, there is a file object with a IsReadOnly field, but the file object is null. I anticipate that I'm not creating the xcel file correctly, but this is the only way I could figure out how to create the file well. Initially I was using a memory stream, but doing that, I ran into issues when the excel file was bigger than 50 rows.

Edit/update: So I initiate the code block by clicking a button "Download as Excel File". The code runs, creating the file, and the user is prompted with a "You have chose to open: thisismyexcelfile.xlsx which is a: XLSX file (size here) from: mywebsite. What should firefox do with this file?" After selecting "Open with OpenOffice Calc" the spreedsheet opens and displays appropriately but is read-only.

Edit/update: I checked the file properties with OpenOffice. Under Properties/Security there is a "Open file Read Only" checkbox, but it is already unchecked and disabled.

Answer 1

From the comments, I was able to verify that saving the file to a location on the disk and opening it directly did not open the file as read-only, implying the problem was not with the code, but the browsers handling of files downloaded from the internet.