How to create .odt files with C#.NET?

Have a look at AODL (see http://odftoolkit.org/projects/odftoolkit/pages/AODL).

• fully managed .NET 1.1 (so it runs on MS.Net and Mono)
• support for text and spreadsheet documents
• create, read, edit, save documents
• ...

EDIT by kame: New link AODL-Wiki

You can check out the OASIS Standards site for information on the ODT standard. From what I've seen, they're using an XML based standard and have an XSD available for the the document standard, so you could use that in conjunction with your own code to build a document file in the proper format.

You might be interested in OpenOffice, UNO CLI Language Binding.