If you have existing documents in Microsoft Word format, it is possible to convert those documents to DITA format. This will allow you to quickly gain many of the benefits of DITA without having to start authoring in Codex from scratch. For example, you can share content between multiple documents, publish documents from a single source to multiple output formats, and minimize translation costs.
Although there are several tools and services available for converting Microsoft Word documents to DITA format, we highly recommend using the XMLmind Word to XML tool. It produces excellent results and is available as a free service: Convert DOCX to DITA 1.2 maps and topics. And if the free service does not meet your requirements, a desktop version provides more capabilities and is available at a very reasonable price ($260 US).