the file you are trying to open is in a different format than specified by the file extension in Asp.Net

Question

the file you are trying to open is in a different format than specified by the file extension c# error when trying to open file in excel.

Here is my code

Answer 1

In case someone else stumbles across this... I needed to convert blobs back into files on-the-fly in C#. Pdf's worked well and excel gave me this same error as OP explains.

This is the code I wrote which handles excel differently from other file types.

Giving excel application/octet-stream with an actual filename solved my issue. Probably not the cleanest way to do it but it was good enough for my purposes.

string theExt = Path.GetExtension(theDoc.documentFileName).ToUpper();

Response.Clear();

if (theExt == ".XLS" || theExt == ".XLSX"){
    Response.ContentType = "application/octet-stream";
    Response.AddHeader("Content-Disposition", string.Format("inline; filename={0}", theDoc.documentFileName));
    }
else{
    Response.ContentType = theDoc.documentMimeType;
    Response.AddHeader("Content-Disposition", string.Format("inline; filename={0}", theDoc.documentTitle));
}

using (MemoryStream stream = new MemoryStream(theDoc.file))
{
    stream.WriteTo(Response.OutputStream);
    stream.Close();
};

Response.End();