How to split PDF WinForms level of bookmarks using C# and VB.NET?

using Syncfusion.Pdf;
using Syncfusion.Pdf.Interactive;
using Syncfusion.Pdf.Parsing;

Imports Syncfusion.Pdf
Imports Syncfusion.Pdf.Interactive
Imports Syncfusion.Pdf.Parsing

//Load the PDF document
PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Sample.pdf");
Dictionary<PdfPageBase, int> pages = new Dictionary<PdfPageBase, int>();
//Maintain collection for page and its index
for (int i = 0; i < loadedDocument.Pages.Count; i++)
{
PdfPageBase page = loadedDocument.Pages[i] as PdfPageBase;
pages.Add(page, i);
}
//Get all the bookmarks
PdfBookmarkBase bookmarks = loadedDocument.Bookmarks;
//Create dictionary with bookmark and split up page range
Dictionary<string, List<int>> splitRange = new Dictionary<string, List<int>>();
for (int i = 0; i < bookmarks.Count; i++)
{
if (bookmarks[i].Destination != null)
{
PdfPageBase page = bookmarks[i].Destination.Page;
 
if (pages.ContainsKey(page))
{
int startIndex = pages[page];
int endIndex = startIndex;
if (i + 1 < bookmarks.Count && bookmarks[i + 1].Destination != null)
{
page = bookmarks[i + 1].Destination.Page;
if (pages[page] - 1 > startIndex)
endIndex = pages[page] - 1;
}
else
{
foreach (string index in splitRange.Keys)
{
int checkStartIndex = splitRange[index][0];
int checkEndIndex = splitRange[index][1];
if (endIndex > checkStartIndex && endIndex < checkEndIndex)
{
endIndex = checkEndIndex;
break;
}
else
endIndex = loadedDocument.Pages.Count - 1;
}
}
 
List<int> range = new List<int>();
range.Add(startIndex);
range.Add(endIndex);
 
splitRange.Add(bookmarks[i].Title, range);
}
}
}
//Split the PDF based on range of bookmark
foreach (string index in splitRange.Keys)
{
int startIndex = splitRange[index][0];
int endIndex = splitRange[index][1];
 
foreach (string key in splitRange.Keys)
{
if (splitRange[key][0] > startIndex && splitRange[key][1] <= endIndex)
{
splitRange[index][1] = splitRange[key][0] - 1; ;
}
}
//Create a new PDF document
PdfDocument document = new PdfDocument();
//Import the pages to the new PDF document
document.ImportPageRange(loadedDocument, startIndex, endIndex);
//Save the document in a specified folder
document.Save(DataPathOutput+"Output_" + index + ".pdf");
//Close the document
document.Close(true);
}
loadedDocument.Close(true);
splitRange.Clear();
pages.Clear();
//Opens the folder where the output documents are saved
System.Diagnostics.Process.Start(DataPathOutput);

'Load the PDF document
Dim loadedDocument As PdfLoadedDocument = New PdfLoadedDocument(( "Sample.pdf"))
Dim pages As Dictionary(Of PdfPageBase, Integer) = New Dictionary(Of PdfPageBase, Integer)
'Maintain collection for page and its index
Dim j As Integer = 0
Do While (j < loadedDocument.Pages.Count)
Dim page As PdfPageBase = CType(loadedDocument.Pages(j), PdfPageBase)
pages.Add(page, j)
j = (j + 1)
Loop
Dim bookmarks As PdfBookmarkBase = loadedDocument.Bookmarks
Dim splitRange As Dictionary(Of String, List(Of Int32)) = New Dictionary(Of String, List(Of Int32))
Dim i As Integer = 0
Do While (i < bookmarks.Count)
If (Not (bookmarks(i).Destination) Is Nothing) Then
Dim page As PdfPageBase = bookmarks(i).Destination.Page
If pages.ContainsKey(page) Then
Dim startIndex As Integer = pages(page)
Dim endIndex As Integer = startIndex
If ((i + 1 < (bookmarks.Count)) _
AndAlso (Not (bookmarks((i + 1)).Destination) Is Nothing)) Then
page = bookmarks((i + 1)).Destination.Page
If ((pages(page) - 1) _
> startIndex) Then
endIndex = (pages(page) - 1)
End If
 
Else
For Each index As String In splitRange.Keys
Dim checkStartIndex As Integer = splitRange(index)(0)
Dim checkEndIndex As Integer = splitRange(index)(1)
If ((endIndex > checkStartIndex) _
AndAlso (endIndex < checkEndIndex)) Then
endIndex = checkEndIndex
Exit For
Else
endIndex = (loadedDocument.Pages.Count - 1)
End If
 
Next
End If
 
Dim range As List(Of Integer) = New List(Of Integer)
range.Add(startIndex)
range.Add(endIndex)
splitRange.Add(bookmarks(i).Title, range)
End If
 
End If
 
i = (i + 1)
Loop
 
'Split the PDF based on range of bookmark
For Each index As String In splitRange.Keys
Dim startIndex As Integer = splitRange(index)(0)
Dim endIndex As Integer = splitRange(index)(1)
For Each key As String In splitRange.Keys
If ((splitRange(key)(0) > startIndex) _
AndAlso (splitRange(key)(1) <= endIndex)) Then
splitRange(index)(1) = (splitRange(key)(0) - 1)
 
End If
 
Next
'Create a new PDF document
Dim document As PdfDocument = New PdfDocument
'Import the pages to the new PDF document
document.ImportPageRange(loadedDocument, startIndex, endIndex)
'Save the document in a specified folder
document.Save((DataPathOutput + ("Output_" _
+ (index + ".pdf"))))
'Close the document
document.Close(True)
Next
loadedDocument.Close(True)
splitRange.Clear()
pages.Clear()
'Opens the folder where the output documents are saved
System.Diagnostics.Process.Start(DataPathOutput)