From what email application?
From Outlook 2007, the first Tab, Message, should included a Attach File (Paperclip icon). You will be prompted to browse to the file location.
Optionally, within Acrobat, from the File Menu
File > Attach to Email will open your default email client with the file already attached.
If you want to attach a PDF file, then you may need to be sure you zip it first or at least be sure that the e-mail package encoding is used for the attachment. PDF files are not ASCII files by are often treated as such by many e-mail packages.