Is it possible to convert a document as a flat file schema as anybody out there has done it? 
I think you can convert a xml document to flat file schema using services in pub.flatFile.generate package. Check the “Programmatically Creating Flat File Schemas and Dictionaries” scetion in flat file schema dev guide.
yes its doable,you can reference xml document to create flatfile dictionary/schema using pub.flatfile:generate folder services.
please see the document “Flat File Schema Developers Guide”.
HTH,
RMG