Print something that is not shown on the screen using wpf.

Im not sure if this is what you want but, 

What you have to do is create a dummy form that's the size of the control you want to print then add the control to the dummy form and show the form and print the control on the dummy. 

Here is how i did it: 

private void printDocument1_PrintPage(object sender, System.Drawing.Printing.PrintPageEventArgs e)
{
    //Create bitmap
    Bitmap image = new Bitmap(dataGridView1.Width, dataGridView1.Height);
    //Create form
    Form f = new Form();
    //add datagridview to the form
    f.Controls.Add(dataGridView1);
    //set the size of the form to the size of the datagridview
    f.Size = dataGridView1.Size;
    //draw the datagridview to the bitmap
    dataGridView1.DrawToBitmap(image, new Rectangle(0, 0, dataGridView1.Width, dataGridView1.Height));
    //dispose the form
    f.Dispose();
    //print
    e.Graphics.DrawImage(image, 0, 0);
}

This will print dataGridView1, even if its not seen on the form.