They actually have a page describing the differences between Surface Office and regular

Your Windows RT tablet does not support Outlook or other desktop email applications such as Mozilla Thunderbird or Opera. Due to this, certain email features available for Office documents in other Office versions are not supported in Office Home & Student 2013 RT:

"Send as … (attachment)" features in the Office Backstage view

Word mail merge features related to email

Sending email links to share slides using the PowerPoint Broadcast Slide Show button on the Slide Show tab

OneNote email share options and email-related options in the Tools/Options menu

Many email-related buttons in the Office Ribbon and Quick Assist Toolbar
Instead, you can open your Windows RT email app or use another email app that may be available from the Windows Store, manually create an email message and attach your document to it.

in addition the following are not supported

But because tablets have special needs for security and mobility, a few features are unavailable in Office Home & Student 2013 RT, including macros, add-ins, and other custom programs written by users or developed by third parties.

And if you have to reset the tablet, it will revert back to the trial version until it has a chance to fully download the regular version again.

Details here

http://office.microsoft.com/en-us/ho...103210361.aspx