Joanne
If by "protect" you mean that you want to encrypt part of the PDF, then this is not possible. What you can do is use digital signatures to protect the data. You can assign specific fields (called a field collection) to a particular signature field. When the signature field is signed, the associated fields are "locked" and if iny of the data is tampered with, the signature will be invalidated.
So the Manager could fill in their portion, sign it and then forward it on to the customer. The customer could view the Manager's data but not change it (intentionally or accidentally)
Regards
Steve