Excel & Word have the ScreenUpdating method thru which a developer can lock the main window from unnecessarily redrawing itself whilst the macro is being executed. This method is however not present in PowerPoint. If left alone, redrawing is not only ugly on the eyes it also takes more time for the macro to reach completion. Hence I created this generic wrapper to lock the window updates.   

' --------------------------------------------------------------------------------
' Copyright ©1999-2018, Shyam Pillai, All Rights Reserved.
' --------------------------------------------------------------------------------
' You are free to use this code within your own applications, add-ins,
' documents etc but you are expressly forbidden from selling or 
' otherwise distributing this source code without prior consent.
' This includes both posting free demo projects made from this
' code as well as reproducing the code in text or html format.
' --------------------------------------------------------------------------------

' UserDefined Error codes
Const ERR_NO_WINDOW_HANDLE As Long = 1000
Const ERR_WINDOW_LOCK_FAIL As Long = 1001
Const ERR_VERSION_NOT_SUPPORTED As Long = 1002

' API declarations for FindWindow() & LockWindowUpdate()
' Use FindWindow API to locate the PowerPoint handle. 
Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
      (ByVal lpClassName As String, _
       ByVal lpWindowName As Long) As Long

' Use LockWindowUpdate to prevent/enable window refresh
Declare Function LockWindowUpdate Lib "user32" _
      (ByVal hwndLock As Long) As Long 
' Use UpdateWindow to force a refresh of the PowerPoint window  
Declare Function UpdateWindow Lib "user32" (ByVal hwnd As Long) As Long

Property Let ScreenUpdating(State As Boolean)
      Static hwnd As Long
      Dim VersionNo As String
      ' Get Version Number
      If State = False Then

        VersionNo = Left(Application.Version, _
                    InStr(1, Application.Version, ".") - 1)
 
' Get handle to the main application window using ClassName
        Select Case VersionNo
        Case "8"  ' For PPT97:
            hwnd = FindWindow("PP97FrameClass", 0&)
        Case "9"  ' For PPT2K:
            hwnd = FindWindow("PP9FrameClass", 0&)
        Case "10" ' For XP:
            hwnd = FindWindow("PP10FrameClass", 0&)
        Case "11" ' For 2003:
            hwnd = FindWindow("PP11FrameClass", 0&)
        Case "12" ' For 2007:
            hwnd = FindWindow("PP12FrameClass", 0&)
        Case "14" ' For 2010:
            hwnd = FindWindow("PPTFrameClass", 0&)
        Case "15" ' For 2013:
            hwnd = FindWindow("PPTFrameClass", 0&)
        Case Else
            Err.Raise Number:=vbObjectError + ERR_VERSION_NOT_SUPPORTED, _
            Description:="Newer version."
            Exit Property
        End Select

        If hwnd = 0 Then
            Err.Raise Number:=vbObjectError + ERR_NO_WINDOW_HANDLE, _
            Description:="Unable to get the PowerPoint Window handle"
            Exit Property
        End If

        If LockWindowUpdate(hwnd) = 0 Then
            Err.Raise Number:=vbObjectError + ERR_WINDOW_LOCK_FAIL, _
            Description:="Unable to set a PowerPoint window lock"
            Exit Property
        End If

      Else
        ' Unlock the Window to refresh
        LockWindowUpdate (0&)
        UpdateWindow (hwnd)
        hwnd = 0

      End If
End Property
 
'Sample Usage:
Sub LongProcessingSub()
' Lock screen redraw
ScreenUpdating=False
' --- Long time consuming code
' Redraw screen again
ScreenUpdating=True
' Also see below article for another example of usage of the code
End Sub

It's fairly simple to open a PowerPoint file (*.ppt) for editing using VBA code however opening a PowerPoint Show (*.pps) file for editing is altogether another matter. Use the Presentation.Open method and it defaults to open the file in Slide Show mode. This might not be desirable. The routine below illustrates a manner of woring around the default behaviour and opening the file for editing. The routine also illustrates the use of the  ScreenUpdating property (code listed above).  

' --------------------------------------------------------------------------------
' Copyright ©1999-2018, Shyam Pillai, All Rights Reserved.
' --------------------------------------------------------------------------------
' You are free to use this code within your own applications, add-ins,
' documents etc but you are expressly forbidden from selling or 
' otherwise distributing this source code without prior consent.
' This includes both posting free demo projects made from this
' code as well as reproducing the code in text or html format.
' --------------------------------------------------------------------------------

Sub OpenPPSForEdit()
On Error GoTo ErrHandle
Dim pShow As Presentation
' Lock the window to prevent refreshing
' See above article example for the code
   ScreenUpdating = False
'Open the show, however use additional flag - WithWindow set to FALSE
   Set pShow = Presentations.Open("C:\sample.pps",  _
                        WithWindow:=msoFalse)
'Open a window now to the presentation for editing
   pShow.NewWindow
' Unlock the window to start refreshing again
   ScreenUpdating = True
   Exit Sub

ErrHandle:
    If Err.Number <> 0 Then
        MsgBox Err.Number & " " & Err.Description, vbCritical + vbOKOnly, "Error"
    End If
End Sub