There is only a format string in the call: "12%1$s". This simply constructs a string with the contents "12" plus the first argument in the argument list using string conversion (basically, creates a string which is "12" concatenated with the second argument of the printf() call.)
All code in my posts, unless a source is explicitly mentioned, is my own.
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com