Depends on what the attachment is I think. All attachments need to be 'detached' into a separate file on the computer, eg in My Docs ...
If the file is a text file, then the contents can be copied and pasted into a normal post. If an image file, then it depends on normal image posting procedures. Other types of file eg music files and video files would need to be uploaded to a host site, and the link then posted for members to view ...
Hopefully, some of the more technically competent can present this a bit better?
Obviously glaringly obvious !!! :D (NOT !)