private void pictureBox1_MouseClick(object sender, MouseEventArgs e)
{
PDFLibrary qp = new PDFLibrary();
qp.UnlockKey(LicenseKey);
qp.LoadFromFile(OriginalFileName);
// Calculate co-ordinates, width of PDF fitted to width of PictureBox
double xpos = ((double)e.X / (double)pictureBox1.Width) * qp.PageWidth();
double ypos = qp.PageHeight() - ((double)e.Y / (double)pictureBox1.Width) * qp.PageWidth();
qp.SetTextSize(24);
qp.SetTextColor(1, 0, 0);
qp.DrawText(xpos, ypos, "A");
qp.SaveToFile(NewFileName);
ShowPDF(NewFileName);
}