Attaching PDFs to emails in Civi (Unknown image format/encoding)

[JohnFF]

When attempting to upload a modest 1.1kb .pdf file as an attachment to a mailing, we get the attached error.

Does it have to be an image as it's called "image upload"? If so, how can we attach a pdf file.

Any idea how we can resolve this?

[clarkac]

Your attached graphic doesn't look like a Civimail screen - more like a Drupal screen.  I tested what you described in Civi & it worked perfectly, but I'm not sure what you are trying to do.  Are you sending a single email, or doing a bulk mailing?