Use RenderImage.Control property for this:
public Control RenderImage.Control {get;set;}
Gets or sets a System.Windows.Forms.Control object,
an image of which is rendered by the current RenderImage object.
The C1.C1Preview.Style.ClientAreaOnly property on the C1.C1Preview.RenderObject.Style
of the current RenderImage object determines whether the whole control, or just its client area,
is rendered.
Note that this property does not cause the current object to render a real live control
that can be used for user input, only a visual image representing the specified control.
For real control behavior, see <RenderInputBase and derived classes.
For instance, the following code previews a document with a snapshot of the form containing c1PrintPreviewControl1:
private void button1_Click(object sender, EventArgs e)
{
RenderImage form = new RenderImage();
form.Control = this;
C1PrintDocument doc = new C1PrintDocument();
doc.Body.Children.Add(aa);
this.c1PrintPreviewControl1.Document = doc;
}
Hope this helps.