supponendo che lo script pdf funzioni prova cosi
codice:
<% 

Dim objFso, objFolder, objFiles, strFolder, strFile 
strPath = "cartella/" 

Set objFso = Server.CreateObject("Scripting.FileSystemObject") 
Set objFolder = objFso.GetFolder(Server.MapPath(strPath)) 
Set objFiles = objFolder.Files 
Set Pdf = Server.CreateObject("Persits.Pdf")

' Open document 1
Set Doc1 = Pdf.OpenDocument( Server.MapPath("doc1.pdf") )

For Each strFile in objFiles
' Open document 2
Set Doc2 = Pdf.OpenDocument( Server.MapPath("/public/"&strFile.name) )

' Append doc2 to doc1
Doc1.AppendDocument Doc2

' Save document, the Save method returns generated file name
Filename = Doc1.Save(Server.MapPath("/public/unione-asp.pdf"), False )

Response.Write "Fatto, il file generato da due pdf e' <A HREF=/public/" & Filename & ">qui</A>
"
Next 

Set objFso = Nothing 
Set objFolder = Nothing 
Set objFiles = Nothing 
Set Doc1 = Nothing
Set Doc2 = Nothing
%>