Safe-guarding your personal identity information is crucial. Online transmission is not always secure.
The open Internet is not secure. Unless you have some special type of secure email or file transfer mechanism, you can consider your regular email as not secure. It is especially hard to control the level of security over the Internet traveling through many countries around the globe. Messages and attachments can be sniffed out and imperceptibly changed.
.PDF files are not secure documents unless they go through a secure file transfer system. Don't let your personal identity get stolen by sending an emailed attachment through regular email. You will find, with voting, it is usually possibly to use the post for transfer of registration and ballot documents.
Unless your election office offers a secure (encrypted or password protected) manner of emailing your application to them we highly suggest that you rely on regular post and/or Fax. Keep in mind, your entire identity is on the federal registration/ballot request form and it is information that should remain closely held.
Note also: For November General Elections, OVF and FedEx Express offer a special highly-discounted ballot return program called: Express Your Vote. Express Your Vote runs starting mid September. During that time, you may visit: www.overseasvotefoundation.org/ExpressYourVote for more information. Voters in approximately 95 countries can take part. Ballot delivery is automatically confirmed.