Legacy Example NOTICE

This article predates the introduction of our PdfDocument class. PdfDocument has a Separate method which is much more efficient for separating two or more PDF files. Support strongly recommends using this newer class for this task

HOWTO: Separate a Multi-Page PDF With Automatic Repair of Damaged PDFs
HOWTO: Combine Multiple PDFs with Automatic Repair of Damaged PDFs
HOWTO: Combine Multiple PDF Files With Fillable Forms (AcroForms)

Main Article Content

When splitting a large pdf into smaller pdf files, it can be difficult to manage the memory needed to complete the operation. Normally the FileSystemImageSource is sufficent to save a large pdf file while not keeping all the frames in memory. However, this prevents you from limiting the frames that are used. Below is an overload of the FileSystemImageSource that allows the setting of a start and finish property.

C#

public class RangedFileSystemImageSource: FileSystemImageSource
{
    private int start;
 
    public int Start
    {
        get { return start; }
        set { start = value; Reset(); }
    }
 
    private int finish;
 
   public int Finish
   {
       get { return finish; }
       set { finish = value; Reset(); }
   }
 
   public RangedFileSystemImageSource(string[] FileNames, bool doAllFrames, int Start, int Finish)
       : base(FileNames, doAllFrames)
   {
       count = 0;
       start = Start;
       finish = Finish;
       this.ImmediateUnload = true;
   }
 
   private int count;
 
   protected override void LowLevelReset()
   {
       count = 0;
       this.Flush();
       base.LowLevelReset();
   }
 
   protected override ImageSourceNode LowLevelAcquire(int index)
   {
       count++;
       return base.LowLevelAcquire(index+start);
   }
 
   protected override bool LowLevelHasMoreImages()
   {
       if (count > finish - start)
           return false;
       return base.LowLevelHasMoreImages();
   }

   protected override bool LowLevelTotalImagesKnown()
   {
       return true;
   }
 
   protected override int LowLevelTotalImages()
   {
       return Math.Max((finish - start) + 1, 0);        /* Return the number of images we intend to return,        unless it would be < 0, then just return 0 */
   }}

VB.NET

Public Class RangedFileSystemImageSource
    Inherits FileSystemImageSource
    Private m_start As Integer
    
    Public Property Start() As Integer
        Get
            Return m_start
        End Get
        Set(ByVal value As Integer)
            m_start = value
            Reset()
        End Set
    End Property
    
    Private m_finish As Integer
    
    Public Property Finish() As Integer
        Get
            Return m_finish
        End Get
        Set(ByVal value As Integer)
            m_finish = value
            Reset()
        End Set
    End Property
    
    Public Sub New(ByVal FileNames As String(), ByVal doAllFrames As Boolean, ByVal Start As Integer, ByVal Finish As Integer)
        MyBase.New(FileNames, doAllFrames)
        count = 0
        m_start = Start
        m_finish = Finish
        Me.ImmediateUnload = True
    End Sub
    
    Private count As Integer
    
    Protected Overloads Overrides Sub LowLevelReset()
        count = 0
        Me.Flush()
        MyBase.LowLevelReset()
    End Sub
    
    Protected Overloads Overrides Function LowLevelAcquire(ByVal index As Integer) As ImageSourceNode
        count += 1
        Return MyBase.LowLevelAcquire(index + m_start)
    End Function
    
    Protected Overloads Overrides Function LowLevelHasMoreImages() As Boolean
        If count > m_finish - m_start Then
            Return False
        End If
        Return MyBase.LowLevelHasMoreImages()
    End Function

    Protected Overloads Overrides Function LowLevelTotalImagesKnown() As Boolean
        Return True
    End Function 
    Protected Overloads Overrides Function LowLevelTotalImages() As Integer
        Return Math.Max((m_finish - m_start) + 1, 0)
        'Return the number of images we intend to return,
        'unless it would be < 0, then just return 0
    End Function
End Class

Original Article:
Q10278 - HOWTO: Split a large pdf file into smaller pdf files while conserving memory