Problems createing a PDF file with multiple files using VB Script

Bottom line up front I'm trying to create a PDF file by combining multiple file types ... PDF, PNG, JPG, HTML, TXT etc.. The code below creates a PDF file but it will only create a PDF file using PDF files. It completely ignores the PNG files.  Any help would be greatly appreciated.

Dim Doc1
Dim Doc2
Dim Doc3
Dim Doc4
Dim Doc5
Dim Doc6
Dim Doc7
Dim Doc8
Dim Doc9

Set Doc1 = CreateObject("AcroExch.PDDoc")
Set Doc2 = CreateObject("AcroExch.PDDoc")
Set Doc3 = CreateObject("AcroExch.PDDoc")
Set Doc4 = CreateObject("AcroExch.PDDoc")
Set Doc5 = CreateObject("AcroExch.PDDoc")
Set Doc6 = CreateObject("AcroExch.PDDoc")
Set Doc7 = CreateObject("AcroExch.PDDoc")
Set Doc8 = CreateObject("AcroExch.PDDoc")
Set Doc9 = CreateObject("AcroExch.PDDoc")

File1 = Doc1.Open("C:\Temp\Single_Page.pdf")
File2 = Doc2.Open("C:\Temp\Page-01.png")
File3 = Doc3.Open("C:\Temp\Page-21.png")
File4 = Doc4.Open("C:\Temp\Page-20.png")
File5 = Doc5.Open("C:\Temp\Page-19.png")
File6 = Doc6.Open("C:\Temp\Page-18.png")
File7 = Doc7.Open("C:\Temp\Page-17.png")
File8 = Doc8.Open("C:\Temp\Page-16.png")
File9 = Doc9.Open("C:\Temp\Page-15.png")

Stack = Doc1.InsertPages(Doc1.GetNumPages - 1, Doc2, 0, Doc2.GetNumPages, 0)
Stack = Doc1.InsertPages(Doc1.GetNumPages - 1, Doc3, 0, Doc3.GetNumPages, 0)
Stack = Doc1.InsertPages(Doc1.GetNumPages - 1, Doc4, 0, Doc4.GetNumPages, 0)
Stack = Doc1.InsertPages(Doc1.GetNumPages - 1, Doc5, 0, Doc5.GetNumPages, 0)
Stack = Doc1.InsertPages(Doc1.GetNumPages - 1, Doc6, 0, Doc6.GetNumPages, 0)
Stack = Doc1.InsertPages(Doc1.GetNumPages - 1, Doc7, 0, Doc7.GetNumPages, 0)
Stack = Doc1.InsertPages(Doc1.GetNumPages - 1, Doc8, 0, Doc8.GetNumPages, 0)
Stack = Doc1.InsertPages(Doc1.GetNumPages - 1, Doc9, 0, Doc9.GetNumPages, 0)

SaveStack = Doc1.Save(1,"C:\Temp\Output\Combined.PDF")