How to prevent user from changing files of a document

Dim objFiles: Set objFiles = Vault.ObjectFileOperations.GetFiles(ObjVer)
' During the creation of the object no test is necessary
if ObjVer.Version > 1 then
	' Getting files of previous version
	Dim ObjVerOld: Set ObjVerOld = ObjVer.Clone()
	ObjVerOld.Version = ObjVerOld.Version-1
	Dim objFilesOld: Set objFilesOld = Vault.ObjectFileOperations.GetFiles(ObjVerOld)

	' If count of files differ then raise exception
	if objFiles.Count <> objFilesOld.count then
		Err.Raise MFScriptCancel, "Es k?nnen keine Dateien hinzugef?gt oder entfernt werden!"
	end if

	Dim found
	For index = 1 To objFiles.Count
		' If a file has a version greater 1 then it was changed => raise exception
		if objFiles.Item(index).FileVer.Version <> 1 then
			Err.Raise MFScriptCancel, "Es k?nnen keine Dateien ver?ndert werden!"
		end if

		' If the GUID of the file has changed then the file was replaced => raise exception
		found = false	
		For indexOld = 1 To objFilesOld.Count			
			if objFiles.Item(index).FileGUID = objFilesOld.Item(indexOld).FileGUID then
				found = true
				Exit for
			end if
		Next
		if found = false then
			Err.Raise MFScriptCancel, "Es k?nnen keine Dateien ausgestauscht werden!"
		end if	
	Next
end if