Tariq, Read the question before answering it! Corey is not asking about digital signatures, he is asking about Certificate Encryption.
Corey, the best way to procure digital certificates (Digital IDs in Acrobat-speak) is to purchase them from a reputable Certificate Authority. You'll need as many digital certificates as you have recipients of your documents. You can also create so-called "self-signed" digital certificates which are less secure but can still do the job. You need to make sure that only intended recipients get these Digital IDs.
Acrobat 8 supports Certificate Encryption. I do not remember whether Acrobat 8 Standard supports it or only Pro.
thank you both, helped to clarify