If I understand your problem correctly, your problem is two-fold: Firstly, you need to find a way to generated documents based on data (mail-merge) and secondly, you might need to print them two.
For document generation you have two basic approaches: template-based and programmatically from scratch. I suppose that you will opt for a template based approach which basically means that you design (in MS Word) a template document (Word, RTF, ...) that acts as a template and contains placeholders and other tags that designate »dynamic« parts of the document. Then, at document generation time, you need a .NET library/processor that you will pass this template document and the data, where the processor will populate the template with the data and return the resulting document.
One way to achieve this functionality would be employing MS Words' native mail-merge, but you should know that this would involve using Office COM and Word Application Automation which should be avoided almost always.
Another option is to build such a system on top of Open XML SDK. This is velid option, but it will be a pretty demanding task and will most probably cost you much more than buying a commercial .NET library that does mail-merge out-of-the-box – been there, done that. But of course, the good side here is that you will be able to tailer the solution to your needs. If you go down this road I recoment that you use Content Controls for tagging documents/templates. The solution with CCs will be much easier to implement than the solution with bookmarks.
I'm not very familliar with the open source solutions and I'm not sury how many there are that can do mail-merge. One I know is FlexDoc (on CodePlex) but its problem is that uses a construct (XmlControl) for tagging that is depricated in Word 2010+.
Then there are commercial solutions. Again I don't know them in detail but I know that the majority of them are a general purpose document processing libraries. Our company has been using this document generation toolkit for some time now and I can say it covers all our »template-based document generation« needs. It doesn't require MS Word at doc generation time, and has really helpful add-in for MS word and you only need several lines of code to integrate it in your project. Templating is very powerful and you can set-up a template in a very short time. While templates are Word documents, you can generate PDF or XPS docs as well. XPS is useful because you can use .NET/WPF prining framework that works with XPS docs to print documents. This is a very high-end solution, but of course, the downside here is that it is not a free solution.