As you may know – if not, there is no more excuse 
– Office 365 integrates the use of RMS – Right Management Services – to protect your document.
To enable and configure RMS for use with Office 365 take a look at http://blog.hametbenoit.info/2013/03/07/office-365-use-right-management-services/
Today, while looking around the Windows Phone Store, I found an RMS client from Microsoft (ONLY for Windows Phone 8) http://www.windowsphone.com/en-us/store/app/rms-sharing/00c487ce-f572-4df9-b6e8-448224230b1e; or for other platform https://portal.aadrm.com/Home/Download
After installing the application, you will have to choose a photo (from a library on your device or by taking one)
Then you will be able to configure your account using your Office 365 login details – NOTE you must have RMS enabled and configured and your account must have be enabled for RMS (licensed) from Office 365 or an RMS individual account – you can register from https://portal.aadrm.com
If your account is not enabled for using RMS, you will get an error message ‘Sorry, you don’t have permission to create new protected content for this organization. Try signing in as a different user, or contacting your administrator for additional permissions.’