Hi Tom,
Use the following code to set Gradient Brush and to draw a rectangle with this graphics property
props.Brush = pdfDoc.CreateGradientBrush(Color.FromArgb(255,187,111), Color.FromArgb(33,67,126), LinearGradientMode.ForwardDiagonal );
pdfDoc.LastPage.Graphics.DrawRectangle ( 0, 0, 300, 200, props );
props.Brush = pdfDoc.CreateGradientBrush(Color.Blue, Color.White , LinearGradientMode.Horizontal );
pdfDoc.LastPage.Graphics.DrawRectangle ( 0,300, 300, 200, props );
Here is sample for your reference which draws two rectangle with different Gradient brush.
GraphicsBrush.zip
Please take a look and let me know if you have any questions.
Thanks,
Ajish.