code: public static PdfTextArray getKernArray(String text, BaseFont font) {
          PdfTextArray pa = new PdfTextArray();
          StringBuffer acc = new StringBuffer();
          int len = text.length() - 1;
          char c[] = text.toCharArray();
          if (len >= 0)
              acc.append(c, 0, 1);
          for (int k = 0; k < len; ++k) {
              char c2 = c[k + 1];
              int kern = font.getKerning(c[k], c2);
              if (kern == 0) {
                  acc.append(c2);
              }
              else {
                  pa.add(acc.toString());
                  acc.setLength(0);
                  acc.append(c, k + 1, 1);
                  pa.add(-kern);
              }
          }
          pa.add(acc.toString());
          return pa;
      }
docs: Constructs a kern array for a text in a certain font
  @param text the text
  @param font the font
  @return a PdfTextArray