Rendering a document uses a workflow component that connects to a previously installed Thumbnail Manager service and "asks" for a document to be processed. The Thumbnail Manager has all the configuration for the renditions that will be produced. Installing a Thumbnail workflow component will allow the configured renditions to be produced for the document being processed. Note that the component requires a binary stream to the data of the file to render, so you’ll need to turn off text extraction (in the case of a standard connector) or write and then read from a binary store (in the case of a background processor) to make it work.