if (v == null)
throw new DocumentException("No field");
if (!af.signatureCoversWholeDocument(fieldName))
throw new DocumentException("Not the last signature");
PdfArray b = v.getAsArray(PdfName.BYTERANGE);
long[] gaps = b.asLongArray();
if (b.size() != 4 || gaps[0] != 0)
throw new DocumentException("Single exclusion space supported");
RandomAccessSource readerSource = reader.getSafeFile().createSourceView();
InputStream rg = new RASInputStream(new RandomAccessSourceFactory().createRanged(readerSource, gaps));
byte[] signedContent = externalSignatureContainer.sign(rg);