Is it possible? How?

Thank you in advance.

I don't think it is possible. What I usually do is either post something in Member Corner with the attachment, and title the thread something like, "For the h.com member".
Alternatively, you may need to send it by e-mail outside of h.com.

Thank you. (What if the article is copyrighted?)

ETA: Searched and found this particular article online. So problem solved for now.

I myself was looking into how to attach a document to a PM this past week and what I learned from the help section is that the system is indeed capable of handling attachments in PMs, but this functionality needs to be activated by the system administrator.

Interesting....