Allow uploading new version of doc to replace content without losing fields

When we have a new version of a contract, we need to be able to upload a new version of the doc , without having to start from scratch. Being able to upload a new version and have all the fields unaffected (we might need to reposition them) will save a LOT OF TIME. I've had to re-create the document more than 5 times now particularly because we cannot preview the doc in the app.