You may need LiveCycle Reader Extension ES2 and LiveCycle Digital Signatures ES2. Here is why...
LiveCycle Reader Extension ES2 is used to "extend" features (on a form by form basis) in the free Adobe Reader. This includes the ability for a user to sign a PDF with Adobe Reader (you can't sign with Reader unless the document\form has been Reader Extended). If your end users have Acrobat Standard or Professional then they can sign without the need for reader extensions.
LiveCycle Digital Signatures ES2 is used (among other things) to sign PDFs on the server side, and to validate the signatures on the signed PDFs on the server side. If you will be "validating" signatures manually then you may not want\need LiveCycle Digital Signatures ES2.