How to save selected images as multi-page PDF

From Dynamic .NET TWAIN v7.0, SaveAsMultiPagePDF is removed. ISave interface in PDF module will do the same job. Below is simple code for that:

using Dynamsoft.PDF;
public partial class Form1 : Form,ISave{
            public object GetAnnotations(int iPageNumber)
        {
            return true;      
        }

        public Bitmap GetImage(int iPageNumber)
        {
            return m_ImageCore.ImageBuffer.GetBitmap((short)dsViewer1.CurrentSelectedImageIndicesInBuffer[iPageNumber]);
        }

        public int GetPageCount()
        {
            return dsViewer1.CurrentSelectedImageIndicesInBuffer.Count; //gets the number of selected images 
        }

        }