Name of PDF & Subject line referencing a cell when emailing PDF

Trying to have the Subject line of email & the name of the PDF attachment to reference a cell. The script has text for the Subject - but would like the Subject line to have text (SHORTS FORM FOR PO ) & reference (C13) The script also has the sheet name for the name of PDF - but would like the name of the PDF to be the contents of cell C13. Can someone help?

function sendSheetToPdfwithA1MailAdress(){ // this is the function to call
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sh = ss.getSheets()[0]; // it will send sheet 0 which is the first sheet in the spreadsheet.
  // if you change the number, change it also in the parameters below
  var shName = sh.getName()
  sendSpreadsheetToPdf(0, shName, sh.getRange('A1').getValue(),"SHORTS FORM FOR PO [C13]", "Please find attached SIW SHORTS RETURN NOTIFICATION FORM");
}
function sendSpreadsheetToPdf(sheetNumber, pdfName, email, subject, htmlbody) {
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  var spreadsheetId = spreadsheet.getId()  
  var sheetId = sheetNumber ? spreadsheet.getSheets()[1].getSheetId() : null;  
  var url_base = spreadsheet.getUrl().replace(/edit$/,'');

  var url_ext = 'export?exportFormat=pdf&format=pdf'   //export as pdf

      + (sheetId ? ('&gid=0' + sheetId) : ('&id=0' + spreadsheetId)) 
      // following parameters are optional...
      + '&size=A4'      // paper size
      + '&portrait=false'    // orientation, false for landscape

  var options = {
    headers: {
      'Authorization': 'Bearer ' +  ScriptApp.getOAuthToken(),
    }
  }

  var response = UrlFetchApp.fetch(url_base + url_ext, options);
  var blob = response.getBlob().setName(pdfName + '.pdf');
  if (email) {
    var mailOptions = {
      attachments:blob, htmlBody:htmlbody
    }
MailApp.sendEmail(
      email, 
      subject, 
      "html content only", 
      mailOptions);
  }
}