I am not quite sure if I understand your question, but it seems like you need some kind of template where you will enter your content.
My thinking goes to OpenXML as the best fit. But since it is rather complex you can save some time by using third party tools.
From my experience, Docentric gives you good value for the money. You can prepare a template in Word and then merge it with data from any source that can fit into .NET object. Your document can be converted to pdf or xps if required.
Templates are generated in MS Word (2007 or newer) using special Docentric Add-in for template generation. All MS Word formatting can be applied here. Placeholders for data are set where the data will appear at runtime.
The process is straight forward so even end users can design reports. Developers then focus on bringing data in from various sources (database, XML). Chech the product documentation for ideas how to use it.