I presume you have an attachment: link in your Org mode file, like this:

[[attachment:foo.pdf]]

You can run (org-attach-expand "foo.pdf") in the Org mode buffer to get the complete path name. That's all you need to create a MIME attachment in GNUS.

I presume you have an attachment: link in your Org mode file, like this:

[[attachment:foo.pdf]]

You can run (org-attach-expand "foo.pdf") in the Org mode buffer to get the complete path name. That's all you need to create a MIME attachment in GNUS.

Adding a src block to your Org mode file like this:

#+begin_src elisp :results drawer
(org-attach-expand "foo.pdf")
#+end_src

will allow you to run the src block to produce the file path which you can then cut-and-paste into GNUS.