Yeah, seems like a Content-Type issue since it should be application/pdf.
Problem on the original sender's end. Garbage In Garbage Out.
Normally I might agree on the GIGO error, but in this case it displays
it correctly, showing it understands what the correct interpretation of the headers is. But then when sending
the message by clicking Forward, it apparently completely rebuilds the attachments, and if no content type is specified, (and I don't think it's mandatory
in the standard?) it sets it to "text", which then causes it to interpret its own creation wrong.
So it's a case of inconsistent behavior. Interpreting by filetype in one instance, and as always text in another.