As you all know, Adobe LiveCycle Designer is a "free" addition shipped with Acrobat 7 Professional. When the product
was first introduced, you needed to purchase Designer apart from Acrobat. However, in version 7 of Acrobat Pro, Designer is included at no additional cost for Windows users only. If you're a Mac user, don't expect to see Designer added as a maintenance upgrade, and quite possibly, you may never see Designer appear on your Mac Desktop. This is not an official Adobe statement, but rather, my own personal speculation.
Adobe LiveCycle Designer is an XML authoring tool used for creating XML forms. For the novice form designer, it's not so important to understand what all the acronyms stand for as it is in knowing that the document you create is very different than the PDF document you edit in Acrobat when creating a PDF form. Acrobat Pro uses AcroForms for forms construction and what we end up with are two very different document structures that, among other things, just don't talk to each other -- at least in a two way conversation.
If you create a form in Designer, save as PDF, and open the file in Acrobat Pro, you can't edit the form fields or document structure in Acrobat. You need to return to Designer for any edits you want to make on your form -- something that's been a pain for many a form designer. On the other hand, you can create a PDF form in Acrobat Pro, open the form in Designer and edit the form. However, once saved from Designer, you can't return to Acrobat to edit your form. Before you begin a project, you need to understand the fundamental fact that a document produced from one authoring tool or the other has limited interoperability.
OK, so you want to stamp your document. Maybe you need to give reviewers some advice about the document's status or sensitivity. This tip from author Ted Padova demonstrates how to add stamps with the Stamp Tool along with related comments.