I'm not sure if this is a problem or not (I'm not at my home box where I can run tests), but I noticed that you seem to be sending two Content-type headers for filenames ending in .pdf:

print "Content-type: application/pdf\n" if ($filename =~ /\.pdf$/);
print "Content-type: application/x-pdf\n" if ($filename =~ /\.pdf$/);
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-rattus
__________
He seemed like such a nice guy to his neighbors / Kept to himself and never bothered them with favors
- Jefferson Airplane, "Assassin"