I moved from using Interop to OpenXML for my Word document manipulation needs, because I wanted to generate Word documents on the server and Microsoft advises not to use Interop for such scenarios - see KB 257757).
Since you have problems with pagination, consider using some 3rd party OpenXML toolkit. Because these toolkits are based on word templates, which get filled with data at runtime, you have all the native functionality of Word, including pagination, which could be set at template design. In your code you don't have to deal with it at all.
Take a look at
this example at Code Project to find out more.