How to programmatically print to PDF file without prompting for filename in C# using the Microsoft Print To PDF printer that comes with Windows 10

To print a PrintDocument object using the Microsoft Print to PDF printer without prompting for a filename, here is the pure code way to do this:

// generate a file name as the current date/time in unix timestamp format
string file = (DateTime.UtcNow.Subtract(new DateTime(1970, 1, 1))).TotalSeconds.ToString();

// the directory to store the output.
string directory = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);

// initialize PrintDocument object
PrintDocument doc = new PrintDocument() {
    PrinterSettings = new PrinterSettings() {
        // set the printer to 'Microsoft Print to PDF'
        PrinterName = "Microsoft Print to PDF",

        // tell the object this document will print to file
        PrintToFile = true,

        // set the filename to whatever you like (full path)
        PrintFileName = Path.Combine(directory, file + ".pdf"),
    }
};

doc.Print();

You can also use this method for other Save as File type printers such as Microsoft XPS Printer