Embedding SQL Server Express into Custom Applications
Rob Walters, from the SQL Team, and I worked on an article for working with SQL Express in Windows Forms applications. There are a couple of quirks when it comes to Click Once that have been included in this MSDN article.
https://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnsse/html/EmSQLExCustApp.asp
Steve