Passing documents in XML

We have a need to transfer documents such as Excel, Word, etc via XML, how does one do that. I am assuming that these would need to be placed into a CDATA section maybe encoding them via BASE64 but I am not sure this is correct or even how to do it. Any code samples, encoding and decoding would be helpful. Also this need includes transferring multiple documents of the types mentioned and that may be a mixture of type of documents, would this cause any problems?

Thanks