Hi, Ben.
Many thanks for your reply.
Can you tell me whether SignatureLogo.pdf must forcibly reside on each user's/employee's computer or whether it is possible to store it in a readily accessible location on a shared network drive/intranet? I ask because, as a large organization in the midst of a rebranding initiative, our visual identity is incredibly important to us, and we'd like to ensure, wherever possible, consistency of, and control over, our corporate brand. (Geesh, that's a lot of commas!) 
Thanks again.