For our employees to get approval on specific online livecycle forms like reimbursment from the manager, the digital signature field looks quite convincing.
How do we implement it with verisign?
Which product from (Verisign) would be best for our needs -
You would need to consult with VeriSign to determine the actual product you should invest in, and how to implement their PKI.
That being said, a digital signature on a PDF is created using an x509 compliant digital certificate. These certificates can be self-signed (created with Acrobat Pro or some other third party utility) or by a Certificate Authority such as VeriSign.
You may also want to look at "electronic" signatures that are supported on PDFs using the signature field object and usually a plugin to Reader or Acrobat. Check out the "electronic and digital signature hardware and software" category at the link: http://www.adobe.com/security/partners/index.html