java program to add digital signature into a pdf file and also encrypt and decrypt it

hi ,

i have written a code to add digital signature to pdf . but when security comes .

currently i have taken care with creating private and public key using key pair generator class.

next i need to encrypt and decrypt on the other side .

i have used currently itext.jar file for adding DigitalSignature to pdf file .

could anyone please help me out asap ....please