Page setup dialog box

Of course it would do that because you create a brand new instance of the dialog using

PageSetupDialog pageSetup = new PageSetupDialog();

What else could you expect?

You really need to re-use the same object over and over. The best and most universal way to do that on-demand using lazy initialization pattern, see http://en.wikipedia.org/wiki/Lazy_initialization[^].

I would simply keep the reference to the dialog as a field of the main form, so the whole picture would look like this:

public class MainForm : Form {

    PageSetupDialog PageSetupDialog {
        get {
            if (fPageSetupDialog == null) {
                fPageSetupDialog = new PageSetupDialog();
                fPageSetupDialog.PrinterSettings = new System.Drawing.Printing.PrinterSettings();
                fPageSetupDialog.PageSettings = new System.Drawing.Printing.PageSettings();
                fPageSetupDialog.EnableMetric = false;
            }
            return fPageSetupDialog;
    } //PageSetupDialog

    PageSetupDialog fPageSetupDialog; //null at first, don't use it directly

    //...

    void SomeMethodWherePageSetupDialogIsUsed() {
        // of the very first call, an instance will be created
        // on other calls, same instance will be used
        // preserving all the previous settings
        PageSetupDialog.ShowDialog();
        //...
    } //SomeMethodWherePageSetupDialogIsUsed

} //class MainForm

—SA