With PDFViewCtrl, you can get a thumbnail Bitmap image for each page in a PDF document.

The following example request thumbnail for page 3:

pdfViewCtrl.ThumbAsync += (sender, e) =>
{
    var bitmap = Bitmap.CreateBitmap(e.Width, e.Height, Bitmap.Config.Argb8888);
    bitmap.SetPixels(e.Buf, 0, e.Width, 0, 0, e.Width, e.Height);
    // use the bitmap
};

// request thumbnail for page 3
pdfViewCtrl.GetThumbAsync(3);

where pdfViewCtrl is an instance of PDFViewCtrl.