问返回PDF页面的SHA256散列

EN

using System.IO;
using System.Text;
using System.Security.Cryptography;
using PdfSharp.Pdf;
using PdfSharp.Pdf.IO;

namespace Syncada
{
    public class PDFDoc
    {

        private PdfDocument pdfDoc;

        public PDFDoc(string path)
        {
            pdfDoc = PdfReader.Open(path,PdfDocumentOpenMode.Import);
        }

        public string GetPageOneHash()
        {

            byte[] hash;

            PdfPage page = pdfDoc.Pages[0];
            using (MemoryStream stream = new MemoryStream())
            {
                PdfDocument doc = new PdfDocument();
                doc.AddPage(page);
                doc.Save(stream,false);

                SHA256 sha256 = SHA256.Create();
                hash = sha256.ComputeHash(stream);
            }

            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < hash.Length; i++)
            {
                sb.Append(hash[i].ToString("X2"));
            }
            return sb.ToString();
        }
    }
}