If you want to encrypt PDFs using a simple password then you should look at the Encryption 1.1 service. This is in the Common category and comes with any of the following LiveCycle modules:
- Barcoded Forms
- Digital Signatures
- Forms
- Output
- PDF Generator
- Process Management
- Reader Extensions
- Rights Management
All of these require the base LiveCycle foundation server parts (which get installed when you install the software).
If you want to encrypt the PDF with something more advanced than a simple password, then you may want to look at the Rights Management software. That module is more of a DRM type encryption which gives you more options for defining policies, recalls, auditing, etc.