I\'m having some difficulty merging multiple word documents together using Microsoft Office Interop Assemblies (Office 2007) and ASP.NET 3.5. I\'m able to merge the documents, b
While adding the documents you are skipping the Template name, that why ut's missing the format.
It should look like
string defaultTemplate="your template name with full path";
OR
Default template name
string defaultTemplate="Normal.dot";
wordApplication.Documents.Add(ref defaultTemplate,............
Use this link as Ref: http://devpinoy.org/blogs/keithrull/archive/2007/05/23/how-to-merge-multiple-microsoft-word-documents-in-c.aspx