Using itext I can get the signing name (Signed By) like this:
fields = reader.getAcroFields();
pk = fields.verifySignature(FieldName);
name = pk.getSignName();
How do I get the signing name using pdfBox?
document.getSignatureDictionaries()
gets the signatures, and PDSignature.getName()
gets the name. To see more, have a look at the ShowSignature.java example from the source code download in the examples subproject.