Set CheckFileExists to true

image_pdfimage_print
   
 

using System;
using System.Windows.Forms;

class MainClass {
    static void Main(string[] args) {
        SaveFileDialog dlg = new SaveFileDialog();
        dlg.CheckFileExists = true;

        if (dlg.ShowDialog() == DialogResult.OK) {
            Console.WriteLine(dlg.FileName);
        }
    }
}