Yes, you can attach any mime type file (See:http://www.sitepoint.com/web-foundations/mime-types-complete-list/ for a full list of Mime types.
However the Mime type is checked so if a file with the extension “.pdf” isn’t a pdf it will be rejected.
As far as the total size of all attachments is concerned, this may be a default value, I don’t recall changing it following our discussion on the number of attachments that were permitted.
If there is a need for larger attachment sizes, then just let me know.
The Forum software also supports “Secure Downloads”, however that option is currently “off”.