4.32 Does LISTSERV properly handle Adobe Acrobat attachments?
Generally, yes. However, when PDF files are sent with quoted-printable encoding, the format of the file may become corrupted, rendering the file unreadable. Using Content-Transfer-Encoding: 7-BIT instead of quoted-printable (or sending the attachment using a Base64 encoding scheme rather than quoted-printable) should solve the problem.
In fairness, this is unlikely to be a problem with modern email clients, unless for some reason they are set to send attachments using uuencode.