Q Whenever my friend attaches a PDF to a message in Mail, it opens and gets embedded in the message, rather than being attached as a file. How can he change that behaviour?
A Some older versions of Mail do this, but the current release (8.2, in Yosemite) now attaches the file as you prefer, as almost every other mail client does.
When using an old version of Mail which by default embeds PDF files in Rich Text format messages, you can turn this off in individual messages using the contextual menu. However there is no preference setting or other way to alter it globally.
If you switch from Rich Text format to Plain Text, these files cannot be embedded and have to remain attached. Third-party mail clients have different features and controls, so if you do not like Mail’s fixed behaviour, look at one of the many alternatives, or take this as a nudge to upgrade to Yosemite.
Updated from the original, which was first published in MacUser volume 30 issue 10, 2014.