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);
int spaceAvailable = (int)(gaps[2] - gaps[1]) - 2;
if ((spaceAvailable & 1) != 0)
throw new DocumentException("Gap is not a multiple of 2");