title: iText - PDFAppearence issue
body: <p>We're using iText to put a text inside a signature placeholder in a PDF. We use a code snippet similar to this to define the Signature Appearence</p>
  
  <pre><code>PdfStamper stp = PdfStamper.createSignature(inputReader, os, '\0', tempFile2, true);
  sap = stp.getSignatureAppearance();
  sap.setVisibleSignature(placeholder);           
  sap.setRenderingMode(PdfSignatureAppearance.RenderingMode.DESCRIPTION);
  sap.setCertificationLevel(PdfSignatureAppearance.NOT_CERTIFIED);
  
  Calendar cal = Calendar.getInstance();
  sap.setSignDate(cal);
  sap.setLayer2Text(text+"\n"+cal.getTime().toString());
  sap.setReason(text+"\n"+cal.getTime().toString());      `
  </code></pre>
  
  <p>Everything works fine, but the signature text does not fill all the signature placeholder area as expected by us, but the area filled seems to have an height that is approximately the 70% of the available space.</p>
  
  <p>As a result, sometimes especially if the length of the signature text is quite big, the signature text does not fit in the placeholder and the text is striped away.</p>
  
  <p>Example of filled Signature:</p>
  
  <p><a href="https://i.stack.imgur.com/nGcWd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nGcWd.png" alt="Example of filled Signature"></a></p>
  
  <p>I looked into the PdfSignatureAppearence class and I found this code snippet in the getApperance() method that is responsible of this behaviour and is invoked when </p>
  
  <pre><code>sap.setRenderingMode(PdfSignatureAppearance.RenderingMode.DESCRIPTION);
  </code></pre>
  
  <p>is being called</p>
  
  <pre><code>      else {
              dataRect = new Rectangle(
                      MARGIN,
                      MARGIN,
                      rect.getWidth() - MARGIN,
                      rect.getHeight() * (1 - TOP_SECTION) - MARGIN);
        }
  </code></pre>
  
  <p>I don't get the reason for that, because I expect that the text could use all the available placeholder height, with the proper margin. </p>
  
  <p>Is there any way to bypass this behaviour?</p>
  
  <p>We are using iText 5.4.2, but also newer version contains same code snippet so I expect that the behaviour will be same.</p>