you are absolutely right xlsx works correctly but when save as PDF has issue
i have attached screen shot which help you to debug .
it does save as PDF only issue is with column Heading that shows only half content (does not show Estimate (draft) if you see C# cod ehow we put this value in to B7 /C7 cells using \n.
sheet1.Cells["B7"].PutValue("COB : " + Common.GetDate_dd_mmm_yyyy(strCobDate) + " \n Estimate (Draft)" );
wb.Save(HttpContext.Current.Response, "RegCapCalcDailySummary_" + String.Format("{0:dd-MMM-yyyy}", Convert.ToDateTime(strCobDate)) + ".pdf", ContentDisposition.Attachment, new OoxmlSaveOptions(SaveFormat.Pdf));
see my generated PDF file .
thanks,
piyush