encrypt and decrypt xml file content

I have large xml file with more than 30 000 lines. It has content like

<?xml version="1.0"?>
   <Nodes>
      <Node>some node name </Node>
      <Node>some node name 2 </Node>
      ...
   </Nodes>

I want to send this xml file with encrypted content to the client manually. Client app (wpf) will load this file and encrypt this file on demand without user intervention (all possible keys will be predefined earlier on this client app).

What method should I use to encrypt and decrypt xml file content?

I was thinking to use http://ift.tt/XOzigv

but since I do not have much experience with this subject I'm asking is this good solution or you would recommend something else?