VBA to Batch Update Folder of MS Word Files with Excel Links

Question

I've got a folder full of MS word docs, all with the same header, containing a couple of fields linked to an excel file to control the project phase and issue date in one spot.

I'm trying to figure out a way to use VBA to loop through all the word docs in this folder, opening them, updating the fields, saving and closing to avoid going through one by one and doing it manually.

Brand new to VBA here and not quite sure what I'm doing (or doing wrong). Here's the code I've pieced together so far based on responses I've seen related to this task. Any help is appreciated on how to improve this/tackle the problem. Happy to provide more info if it helps.

Receiving error "Object variable or With block variable not set" on line "Set oWordDoc = oWordApp.Documents.Open(sFileName)"

Thanks!

Update: Thank you everyone for the help, working code added below.

Sub Sample()
Dim oWordApp As Object, oWordDoc As Object, rngStory As Object
Dim sFolder As String, strFilePattern As String
Dim strFileName As String, sFileName As String

'> Change this to the folder which has the files
sFolder = Dir(Range("A20").Value)

'> This is the extention you want to go in for
strFilePattern = "*.doc"

'> Establish Word application object
On Error Resume Next
Set oWordApp = GetObject(, "Word.Application")

If Err.Number <> 0 Then
    Set oWordApp = CreateObject("Word.Application")
End If
Err.Clear
On Error GoTo 0

oWordApp.Visible = True

'> Loop through the folder to get the word files
strFileName = Dir$(sFolder & strFilePattern)
Do Until strFileName = ""
    sFileName = sFolder & strFileName

    '> Open the word doc
    Set oWordDoc = oWordApp.Documents.Open(sFileName)

    '> Update Fields
   
     oWordDoc.Fields.Update
        


    '> Close the file after saving
    oWordDoc.Close SaveChanges:=True

    '> Find next file
    strFileName = Dir$()
Loop

'> Quit and clean up
oWordApp.Quit

Set oWordDoc = Nothing
Set oWordApp = Nothing
End Sub

Updated Working Code:

Sub UpdateSpecHeaders()
Dim oWordApp As Object, oWordDoc As Object
Dim sFolder As String, strFilePattern As String
Dim strFileName As String, sFileName As String

'> Folder containing files to update
sFolder = Range("A20").Value


    '> Identify file extension to search for
strFilePattern = "*.doc"


'> Establish a Word application object
On Error Resume Next
Set oWordApp = GetObject(, "Word.Application")

If Err.Number <> 0 Then
    Set oWordApp = CreateObject("Word.Application")
End If
Err.Clear
On Error GoTo 0

oWordApp.Visible = True


'> Loop through the folder to get the word files
strFileName = Dir$(sFolder & strFilePattern)
Do Until strFileName = ""
    sFileName = sFolder & strFileName

    '> Open the word doc
    Set oWordDoc = oWordApp.Documents.Open(sFileName)
    
    Application.DisplayAlerts = False


    '> Update Fields
    oWordApp.ActiveDocument.Fields.Update
     

    '> Save and close the file
    oWordDoc.Save
    oWordDoc.Close SaveChanges:=True
    
        
    '> Find next file
    strFileName = Dir$()
Loop

'> Quit and clean up
oWordApp.Quit

Set oWordDoc = Nothing
Set oWordApp = Nothing

End Sub