Extracting pages from one PDF and adding them into new PDF

Hello,

I am looking to extract PDF pages from an existing document into a new document using VB.NET and the Adobe Acrobat Library/API (Interop.Acrobat).  Essentially, I want to take a large amount of pages and break them down into separate documents. For example. I want to break down a 100 page document into 2 50 page documents, etc.

I have written some code below; once I can write into a single PDF, I will them loop and write out to as many PDF documents as I need.  Line 33 returns nothing, as I assume the underlying document I am attempting to access has not been created.  The other code I have written accesses an already created document using the .Open() method.  What do I need to do in order to create the document object before I step to Line 33?  I do not see any methods under _acroDoc2 to create a new PDF, only to Open() existing documents.

My code is as follows:

        Dim filePath = "Path/To/Source/File"


        'create adobe and get document
        Dim _acroDoc As New Acrobat.AcroAVDoc()
        Dim _myAdobe As New Acrobat.AcroApp()
        _myAdobe.Hide()


        Dim _pdDoc As Acrobat.AcroPDDoc
        _pdDoc = Nothing
        _acroDoc.Open(filePath, "sourceFile")
        _pdDoc = DirectCast(_acroDoc.GetPDDoc(), Acrobat.AcroPDDoc)


        'retrieve total page count from document
        Dim pageCount = _pdDoc.GetNumPages()


        'determine how many pages per document
        'Dim pdfPageLength = Math.Floor(maxPagesAllowed / letterRecord.DocumentPageLength) * (letterRecord.DocumentPageLength)
        Dim pdfPageLength = 50


        'create new instance of adobe to extract pages from original instance
        Dim _acroDoc2 As New Acrobat.AcroAVDoc()
        Dim _myAdobe2 As New Acrobat.AcroApp()
        _myAdobe2.Hide()


        'get second empty document instance to write a new PDF
        Dim _pdDoc2 As New Acrobat.AcroPDDoc
        _pdDoc2 = DirectCast(_acroDoc2.GetPDDoc(), Acrobat.AcroPDDoc) 'this line equals nothing as document isnt instantiated


        Dim startPage As Double = 0
        Dim endPage As Double = pdfPageLength


        'insert pages from original PDF document instance
        _pdDoc2.InsertPages(startPage, _pdDoc, startPage, endPage, 0)


        'save and close
        Dim savePath = "C:\Users\myusername\Desktop\newPDF.pdf"
        Dim savemergefile = _pdDoc2.Save(1, savePath)