Cannot see attachment if Content-Type is application/octet-stream;

Hi. I received an important mail from a certified server expecting a pdf in it.
I couldn’t find it.
I forwarded the email to Thunderbird and it appeared.
I checked the source of the mail, the pdf was nested inside as:
Content-Type: application/octet-stream;
Content-Disposition: attachment
Content-Transfer-Encoding: base64

Why k9 doesn’t show the pdf if is attached as octet-stream?
Other mail client visualize it correctly.

thank you guys