Here's my suggested culprit:

Set msgInternal = CreateItemFromTemplate(tempFolder & tempFileName)
A message with a PDF attachment is being "re-created" without the assistance of Acrobat, resulting in corruption to the attachment, I suspect. If I open a message with a message attachment and manually drag and drop it into, say my Inbox, I can run the macro and it saves and prints any PDF attachments without corruption. All I need is to be able to copy the message within the message into a particular Outlook folder and then process it from there with the macro...?