Several users have reported that they are unable to send Pages, Numbers or Keynote file attachments via email (Google Gmail or Yahoo etc) after upgrading to OS X 10.9 (a.k.a. Mavericks). Please note that the cause of this problem/bug is still unknown. If you are having this problem, here are some basic steps you might try:
1. Zip your document (compressed version) and email the zip file.
2. Export to previous version. For instance, if this is a .Pages file, click File > Export To > Pages ’09. Save this new file and and send it.
3. Convert your document to PDF or Word etc and then send it (File > Export To).
More:
Mail and Mail App Troubleshooting and Fixes