Prashanth Enduri wrote:
1) I am using the below code to sign the PDF digitally. After adding the signature it showing that the signature as "Validity Unknown".

What certificate did you use?

     how to currect this one ?

Buy a certificate from a CA that has its root certificate
in Adobe Reader.

2) And how to validate the signature, whether signature from currect person or not?

Read chapter 16 of the book 'iText in Action'.
Also: if the signature is added with for instance a self-signed
certificate, you'll never know if the person who signed the PDF
is really who he claims he is. Again: to be sure, the signer
should use a certificate from a CA that ensures people are who
they claim to be.

3) i having a requirement in that 1st person will sign after that next person will edit that pdf and he also sign that pdf. how to verify in this case?

In that case, you'll make a PDF that has different versions.
In chapter 16 of the book, you'll learn how to find out who
signed which version of the PDF.
br,
Bruno

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