This method takes all of the PDFs in the folder c:acrobatdocstomerge and
merges them together to form a file called complete.pdf.

This code sample is posted here for the general benefit of the PDF development community. Attribution and usage guidelines are as noted in the code source; please respect the wishes of the author when using this code.

Option Explicit ' Force variable declaration
' Author : Planet PDF
' E-Mail: info@debenu.com
' Date : 08 March 1998
' Description: JoinAllAcrobatDocsInDir
' This vb method uses IAC to join all PDF documents in a folder 
' to a predetermined filename
' This method / function should be extended to suit the requirements
' of an organisation
Public Const PDF_WILDCARD = '*.pdf'
Public Const PDF_DIRECTORY = 'c:acrobatdocstomerge'
Public Const JOIN_FILENAME = 'complete.pdf'
Sub JoinAllAcrobatDocsInDir()


    Dim AcroExchApp As Object, AcroExchPDDoc As Object, _
        AcroExchInsertPDDoc As Object
    Dim strFileName As String, strPath As String
    Dim iNumberOfPagesToInsert As Integer, _
        iLastPage As Integer
    Set AcroExchApp = CreateObject('AcroExch.App')
    Set AcroExchPDDoc = CreateObject('AcroExch.PDDoc')

' Show the Acrobat Exchange window
    AcroExchApp.Show

' Set the directory / folder to use
    strPath = PDF_DIRECTORY

' Get the first pdf file in the directory
    strFileName = Dir(strPath + PDF_WILDCARD, vbNormal)

' Open the first file in the directory
    AcroExchPDDoc.Open strPath + strFileName
    
' Get the name of the next file in the directory [if any]
    If strFileName <> '' Then
        strFileName = Dir
   
    ' Start the loop.
        Do While strFileName <> ''
    
    ' Get the total pages less one for the last page num [zero 
based]
            iLastPage = AcroExchPDDoc.GetNumPages - 1
            Set AcroExchInsertPDDoc = CreateObject('AcroExch.PDDoc')
        
        ' Open the file to insert
            AcroExchInsertPDDoc.Open strPath + strFileName

        ' Get the number of pages to insert
            iNumberOfPagesToInsert = AcroExchInsertPDDoc.GetNumPages

        ' Insert the pages
        AcroExchPDDoc.InsertPages iLastPage, AcroExchInsertPDDoc, 0, 
iNumberOfPagesToInsert, True
    
        ' Close the document
            AcroExchInsertPDDoc.Close
    
       ' Get the name of the next file in the directory
            strFileName = Dir
             Loop
        
    ' Save the entire document as the JOIN_FILENAME using SaveFull 
[0x0001 = &H1]
        AcroExchPDDoc.Save &H1, strPath + JOIN_FILENAME

End If

' Close the PDDoc
    AcroExchPDDoc.Close
        
' Close Acrobat Exchange
    AcroExchApp.Exit
End Sub