Something like this can be done by linking an Evernote account with RTM, but it is rather convoluted. I for one wish that RTM would make this happen - straight up support for attachments like docs, pdfs, audio, etc. Seems like all the competitors offer this.

There is no facility for direct attachments to tasks, but as @potts7 says you can link an Evernote note to a task.
Right click on a note in Evernote, click "Copy Note Link" then paste the note link into either the URL field of a task or into the notes section of a task.
When you click on the note link in the task it will open the note in Evernote (if you have it running on a PC) or open it in a browser (or both).

Hope this helps.

I guess the reason RTM does not offer it is because it would potentially take up a lot of space on the RTM servers.

Txs for the info :-)

I have used URL fields to link to various files in dropbox, google drive, one driver, emails, etc.

RTM and evernote integrate with each other, link your evernote and RTM accounts together. After that, adding a reminder to an evernote note will automatically generate a new task in RTM with a link to that note.

I'm a new user who is used to having attachments to tasks (i.e. Outlook). Highly recommend offering this feature

I sync my information with Dropbox. While I'm working in my notebook, if needed, I keep Dropbox opened. When I need to attach a file to a task, I select the file in Dropbox, click on Share button, click on Copy link button, and paste that link to any task/note in RTM. That doesn't use any significant space and it's kind of practical. Hope this helps.