Download Documents to Go Main App. Once you do that, adding an attachment to emails will give you a filetype option rather than going immediately to pictures to attach.
Assuming you've already placed your documents onto a folder on your SD card, once you select Documents to Go as the attachment type, just find the folder where you stored your documents and you should be able to attach.
This shouldnt require the full version of Docs to Go, but you sound like you might want the additional editing ability. It's half off right now, for what its worth.
Of note, i actually didn't get the attachment type option until after I used Documents to Go once.
Hope that helps. If you are unsure how to store your documents to your SD card, search the forum to learn how to "Mount your SD Card"