title: How to get multiple headers/footers in a document with Google Apps Script
body: <p>Im trying to replace a text in a Google Document header which has "Different first page Header/Footer" active. I succesfully replace text in any other page header except on first page.
  ...</p>
  
  <pre><code>var something = "Some string.";
  var copyId = DriveApp.getFileById(docTemplate).makeCopy(name).getId();
  var copyDoc = DocumentApp.openById(copyId);
  var copyHeader = copyDoc.getHeader();
  copyHeader.replaceText('keySomething', something);
  </code></pre>
  
  <p>...</p>
  
  <p>I looked at the documentation but didn't see how to do it. I even tried with "getHeaders()" (in plural) but that class doesn't exist.
  How I can replace the text in the first page header/footer?</p>
  
  <p>Thanks,</p>
  
  <p>Iván</p>