Network printers ignoring number of copies sent programatically

Question

The setup - a local Windows 10 PC has multiple network printers installed. A GUI C# WinForm application (.NET) is constantly running in the background, and occasionally downloads a PDF file from a predefined URL (read from an *.ini file).

The problem occurs when the said PDF file is printed. Instead of accepting the number of copies sent from the application, the printer keeps printing just one copy of the file.

This is the relevant part of my code:

        string webPrinter = "HP LaserJet PCL 6"; // is set in another part of the code
        string iniFilePrinter = "hp LaserJet 1320 PCL 5"; // is set in another part of the code - read from the ini file
        string dirName = "C:\\mydir";
        string newDocName = "mydoc.pdf";
        short numCopies = 1;

        if(event1 == "event1") {        // taken from another part of the code
            numCopies = webNumCopies;   // taken from another part of the code
        } else if(event2 == "event2") {
            numCopies = iniNumCopies;   // taken from another part of the code - read from the ini file
        }

        var path = dirName + "\\" + newDocName;

        try
        {
            using (var document = PdfiumViewer.PdfDocument.Load(path))
            {
                using (var printDocument = document.CreatePrintDocument())
                {
                    System.Drawing.Printing.PrinterSettings settings = new System.Drawing.Printing.PrinterSettings();
                    string defaultPrinterName = settings.PrinterName;

                    printDocument.DocumentName = newDocName;
                    printDocument.PrinterSettings.PrintFileName = newDocName;
                    printDocument.PrinterSettings.Copies = numCopies;
                    printDocument.PrintController = new System.Drawing.Printing.StandardPrintController();
                    printDocument.PrinterSettings.PrinterName = webPrinter;

                    MessageBox.Show("Before: " + printDocument.PrinterSettings.Copies.ToString() + " --- " + newDocName);

                    if (!printDocument.PrinterSettings.IsValid)
                    {
                        printDocument.PrinterSettings.PrinterName = iniFilePrinter;

                        if(!printDocument.PrinterSettings.IsValid)
                        {
                            printDocument.PrinterSettings.PrinterName = defaultPrinterName;
                        }
                    }

                    MessageBox.Show("After: " + printDocument.PrinterSettings.Copies.ToString() + " --- " + newDocName);

                    printDocument.Print();
                }
            }
        }
        catch (Exception ex) {
            MessageBox.Show(ex.Message);
        }

The exception has never been triggered, and the print succeeds on every single try. Changing the number of copies within if/else also happens when the conditions are met, and the MessageBox.Show() parts of the code do show the expected number of copies (2,3,7, anything but 1, when it's not supposed to be 1) immediatelly before invoking printDocument.Print().

I've also tried printing unrelated documents from various other programs (MS Word, various custom applications, PDF readers and the like), and the number of copies has always been 1. However, software like Google Chrome or FireFox manage to get things printed in the specified number of copies.

I was thinking that there might be something about the printer's setting which makes it ignore the number of copies sent. Based on that assumption, I've checked the settings of all of the printers, and have found that the number of copies is actually set to 1.

If that is indeed the cause of my problem, how can I bypass that setting (without actually changing it), the way that Google Chrome and Firefox seem to be able to do it? I know that I could probably change that limit programmatically (set it to my number of copies, and then change it back to the original value, once the printing has been completed), but that doesn't seem like the proper way of doing it.

EDIT

I've expanded my code by including a print dialog, like this:

                PrintDialog printDlg = new PrintDialog();
                printDlg.Document = printDocument;
                printDlg.AllowSelection = true;
                printDlg.AllowSomePages = true;

                if (printDlg.ShowDialog() == DialogResult.OK)
                {
                    printDocument.Print();
                }

Still, the results are the same - even when the user changes the number of copies within the print dialog, the printer ignores them. The same code was tested on another (local) printer, connected to an unrelated Windows 10 PC, and there the number of copies from the dialog was not ignored.

I've also noticed that the print dialog from my application, and that from notepad.exe are different (image below). Is there a way for me to call up the same print dialog notepad.exe uses? The reason I'd like to do this, is because that one gets the job done (xy number of copies in the print dialog, xy number of copies printed).