Using iText, I've successfully created a document containing an empty signature field. Now I want to allow people to sign this document in Adobe Reader. I've read that I need to Reader enable my document, but I can't find how to do this using iText.
This is only possible using Adobe Software. The technology that is used to enable a PDF document is based on public-key cryptography, where the viewer of the document (in this case Adobe Reader) has the public key and the authoring software for the document has the corresponding private key. Because iText (and for that matter any other non-Adobe software) has no access to Adobe's private key, you can only enable documents using Adobe products such as LiveCycle Reader Extensions or Acrobat Professional.
Click this link if you want to see how to answer this question in iText 5.