How could I display a pdf file as an image in C# winform?

I'm new in C# and I have create a scanner application by C# winform. Now I'm having a problem that when i use treeview for a folder and click in item inside (all items inside are images and pdf file). All image file format display normal in picture box but when i try to display for pdf file it not working, my app just notice that is not a pdf file but the file i click in totally in a pdf file. Does anyone have some advise

<pre> private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
 {
     if (e.Node != null && e.Node.Tag != null && File.Exists(e.Node.Tag.ToString()))
     {
         string selectedFile = e.Node.Tag.ToString();
         if (File.Exists(selectedFile))
         {
             if (IsImageFile(selectedFile))
             {
                 try
                 {
                     if (IsPdfFile(selectedFile))
                     {
                         if (selectedFile.ToLower().EndsWith(".pdf"))
                         {
                             using (PdfiumViewer.PdfDocument document = PdfiumViewer.PdfDocument.Load(selectedFile))
                             {
                                 int imageIndex = treeView1.SelectedNode.Index;
                                 using (Bitmap image = (Bitmap)document.Render(imageIndex, 300, 300, true))
                                 {
                                     pictureBox1.Image = new Bitmap(image);
                                 }
                             }
                         }
                     }
                     else
                     {
                         pictureBox1.Image = Image.FromFile(selectedFile);
                     }
                 }
                 catch (Exception ex)
                 {
                     MessageBox.Show("Error loading file: " + ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                 }
             }
             else
             {
                 MessageBox.Show("Selected file is not an image or PDF.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
             }
         }
         else
         {
             MessageBox.Show("Selected file does not exist.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
         }
     }
 }

 private bool IsImageFile(string fileName)
 {
     string[] validExtensions = { ".jpg", ".jpeg", ".png", ".gif", ".bmp" };
     string extension = Path.GetExtension(fileName);
     return validExtensions.Contains(extension.ToLower());
 }

 private bool IsPdfFile(string fileName)
 {
     string[] pdfExtensions = { ".pdf" };
     string extension = Path.GetExtension(fileName);
     return pdfExtensions.Contains(extension.ToLower());
 }

 private void PopulateTreeView(string directory, TreeNode parentNode)
 {
     if (parentNode == null)
     {
         treeView1.Nodes.Clear();
     }

     DirectoryInfo directoryInfo = new DirectoryInfo(directory);
     TreeNode node = new TreeNode(directoryInfo.Name);
     node.Tag = directoryInfo.FullName;

     node.ImageIndex = 0;
     node.SelectedImageIndex = 0;

     if (parentNode == null)
     {
         treeView1.Nodes.Add(node);
     }
     else
     {
         parentNode.Nodes.Add(node);
     }

     try
     {
         foreach (var dir in directoryInfo.GetDirectories())
         {
             PopulateTreeView(dir.FullName, node);
         }

         foreach (var file in directoryInfo.GetFiles())
         {
             TreeNode fileNode;
             if (IsImageFile(file.FullName))
             {
                 fileNode = new TreeNode(file.Name);

                 fileNode.ImageIndex = 1;
                 fileNode.SelectedImageIndex = 1;
             }
             else if (IsPdfFile(file.FullName))
             {
                 fileNode = new TreeNode(file.Name);
                 fileNode.ImageIndex = 2;
                 fileNode.SelectedImageIndex = 2;
             }
             else
             {
                 continue;
             }
             fileNode.Tag = file.FullName;
             node.Nodes.Add(fileNode);
         }
     }
     catch (UnauthorizedAccessException)
     {
         node.Nodes.Add("Access denied");
     }
     catch (Exception ex)
     {
         node.Nodes.Add("Error: " + ex.Message);
     }
 }