Multiple documents send to default printer queue order

Question

I am developing an application which is work as print agent without getting user interaction. In there, I have to consider about below conditions.

• Download file shouldn't be access for user.
• file sould be deleted after print it.
• The download document could be either Image/PDF or word.docx
• First downloaded file should be print first.

So far I able to complete as follow. - watcher method created to catch up new download file.

public void catchDocuments()
        {
            if (!string.IsNullOrEmpty(Program.docDirectory))
            {
                file_watcher = new FileSystemWatcher();
                file_watcher.Path = Program.docDirectory;
                file_watcher.EnableRaisingEvents = true;
                file_watcher.Created += new FileSystemEventHandler(OnChanged);
            }            
        }

when new file came, it will fire Onchange event and print document.

string extension = Path.GetExtension(args.FullPath);
if (extension.Equals(@".png") || extension.Equals(@".jpeg") || extension.Equals(@".jpg"))
{
    docCtrl.imageToByteArray(nFile);
    docCtrl.printImage();
}
else if (extension.Equals(@".pdf"))
{                     
    docCtrl.PrintPDF(nFile);
}

But My problem is, When another files download before complete print process of downloaded file, Application will not work properly.

I used print option as follow.

//For Image printing
public void printImage()
{     
    System.Drawing.Printing.PrintDocument pd = new System.Drawing.Printing.PrintDocument();
     pd.PrintPage += new PrintPageEventHandler(PrintPage);        
    PrintDialog pdi = new PrintDialog();
    pdi.Document = pd;
    pdi.PrinterSettings.PrinterName;
    pd.Print();    
}

    //For PDF Printing
public void PrintPDF(string path)
    {
       PrintDialog pdf = new PrintDialog();
       Process p = new Process();
       pdf.AllowSelection = true;
       pdf.AllowSomePages = true;
       p.EnableRaisingEvents = true; //Important line of code
       p.StartInfo = new ProcessStartInfo()
         {
           CreateNoWindow = true,
           Verb = "print",
           FileName = path,
         };
       p.Start();
       p.WaitForExit();
       p.Close();
    }

how could I overcome this issue. I'll be really appreciate your good thoughts.