you can send a file from gmail. just be sure to go to basic html from gmail. open gmail on pb, scroll to bottom of messages and you will see viewing choices "view gmail in mobile | basic html | desktop". choose basic html. when you compose a message you will see the option to attach a file.
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Files & Folders has a handy send-file-via-email feature that works well with GMail and many other mail services. You might like to take the trial version for a spin:
Files & Folders, the unified file & cloud manager for PlayBook and BB10 with SkyDrive, SugarSync, Box, Dropbox, Google Drive, Google Docs. Free 3-day trial! - Jon Webb - Innovatology - Utrecht, Netherlands