Open PDF Files, Save With New Security Settings

I am trying to use a shell command to dig into a specified directory (and ideally all sub-directories) and open every pdf file and re-save with security settings changed (adding a password to prevent printing). I can't seem to get the shell command to run from where it is:

Option Explicit

Sub OpenPDFFilesAndSave()
'opens every pdf file in a directory
Dim FSO As Object, Fld As Object, Fil As Object
Dim MainFolderName As String, i As Integer
Dim RetVal As Variant

Set FSO = CreateObject("Scripting.FileSystemObject")
MainFolderName = "C:Test"
Set Fld = FSO.GetFolder(MainFolderName)
For Each Fil In Fld.Files
i = i + 1
RetVal = Shell("C:Program FilesAdobeAcrobat 7.0
_&AcrobatAcrobat.exe MainFolderName & " " & Fil. Name")
Next
'have to add save the file, and change the print settings but not figured that out yet
End Sub