Yes – it’s possible by linking to the pdf attachment on a private, or password-protected, page.
Thanks esmi. I assume that means the pdf will be stored in a public folder, so if someone has the url they can just go ahead and download anyway? Is there a way to protect a folder so only those logged in can access its contents? Sorry if I’ve misunderstood / explained badly, I’m very new to this game.
I assume that means the pdf will be stored in a public folder
Correct.
Is there a way to protect a folder so only those logged in can access its contents?
You could use a plugin like WP-DownloadManager: http://ww.wp.xz.cn/extend/plugins/wp-downloadmanager/
But that does seem a little OTT for a single download. Another option might be to archive the pdf file in a password-protected zip file and then only make the zip password available to members via a private page.