c# Export Object Into New A Type Of Files

c# Export Object Into New A Type Of Files

i will explain by an example, a PSD file is a file where photoshop save a
project, a DOC file is a file where Office Save a Document...
I am making an application where i work with object and i want to export
my object into a new type of files (for exemple TQA : Test Question
Answer), and i want my application to be the only program that can open
that file.
static class TestQuestionAnswer
{
public string Question;
public string Answer;
//...initiating of the Question and Answer
//...Exporting the object to a TQA file..??
}
any ideas ?