Pulling attachments from Document Category

I need to pull all of the documents from a process and send them in byte array format to an external web service for another product.   I'm able to pull the IncidentDocumentId value for the process in question and get the Document ID's for each document, however I'm not seeing anything that gives me the actual data for the file in question.  Can anyone point me in the right direction?   Also, I'm assuming the actual file data when outputed to a variable will be in byte array format?