How are you trying to mail it Outlook, Gmail, Yahoo or another service? Usually most services have a paperclip icon when composing an email that lets you attach a file. Click the icon, navigate to where your file is stored, click the file and then click OK. If this is in a work environment they may have set limit on the size of file attachments sent through the network and you would need to check with you network admin on what those limits are.
You may also have problems if you have an invalid email address.
More details are need as to what the problem is.
IS it finding and attaching the document to an email or in the actual sending process