title: PDFbox, exception on fonts
body: <p>I've write a simple code for edit content of a form inside a pdf. Everithing works fine (new pdf is created with modified form) but a strange excetpion about fonts were thrown. This is my code:</p>
  
  <pre><code>try {
          PDDocument pdfDoc = PDDocument.load("/home/giozh/universita/schedepazienti.pdf");
          PDDocumentCatalog docCatalog = pdfDoc.getDocumentCatalog();
          PDAcroForm acroForm = docCatalog.getAcroForm();
  
          PDField field = acroForm.getField("dx1");
          if (field != null) {
              field.setValue("asd");
          } else {
              System.err.println("No field found with name:" + "applicationPrepaid[0].#pageSet[0].Pagina1[0].txtFirstName[0]");
          }
          pdfDoc.save("/home/giozh/universita/schedepazienti1.pdf");
          pdfDoc.close();
      } catch (IOException ex) {
          Logger.getLogger(Prove.class.getName()).log(Level.SEVERE, null, ex);
      } catch (COSVisitorException ex) {
          Logger.getLogger(Prove.class.getName()).log(Level.SEVERE, null, ex);
      }
  </code></pre>
  
  <p>and this is exception:</p>
  
  <pre><code>Grave: error while creating a font
  java.io.IOException: Cannot create font as /SubType is not set.
  at org.apache.pdfbox.pdmodel.font.PDFontFactory.createFont(PDFontFactory.java:88)
  at org.apache.pdfbox.pdmodel.PDResources.getFonts(PDResources.java:203)
  at org.apache.pdfbox.pdmodel.interactive.form.PDAppearance.getFontAndUpdateResources(PDAppearance.java:439)
  at org.apache.pdfbox.pdmodel.interactive.form.PDAppearance.setAppearanceValue(PDAppearance.java:268)
  at org.apache.pdfbox.pdmodel.interactive.form.PDVariableText.setValue(PDVariableText.java:131)
  at prove.Prove.main(Prove.java:37)
  </code></pre>
  
  <p>(line 37 is where i call setValue() method)
  how can i fix it?</p>