How you write it depends on what you mean by "open a CV file"
If you have it as a Word document for example, then you would just use Process.Start:
private void butOpenCV_Click(object sender, EventArgs e)
{
string cvToOpen = @"D:\Temp\ThisBlokesCV.docx";
Process.Start(cvToOpen);
}
If you want to open it into your application, then we would need more information.