On creating a instance of PDFReader for the given PDF, openPDF (itext) is not able to read the signature name. But if using newer version of openPDF, I can see the signature name.
Also, If I open the pdf in text editor I can still see the annotation as below
/FT /Sig
/Type /Annot
/Subtype /Widget
/F 132
/T (Signature1)
/V 249 0 R