saving a word docx file as a txt in excel VBA and getting runtime error 438

I am trying to save a word docx file as a txt using excel VBA. However the error 438 comes up when i try to save as the new string

Sub SaveToTXT()

    Dim wordDoc As Object
    Set wordDoc = CreateObject("Word.Application")
    
    Dim wordPath As String
    
    wordPath = "C:\Users\file"
    
    wordDoc.Documents.Open wordPath
    
    wordDoc.Visible = False
    
    wordPath = Replace(wordPath, ".docx", ".txt")
       
    wordDoc.SaveAs2 (wordPath)
    
    wordDoc.Quit

End Sub

Its a bad idea to use late binding when you are new to VBA because late binding doesn't give you any intellisense. Set a reference to Ms word so that you can get full intellisense (In the IDE use Tools.References then make sure that MS Word xx.x object library is ticked).

The code below should get you closer to what you want

Sub SaveToTXT()

    Dim myword As Word.Application
    Set myword = New Word.Application
    
    Dim myPath As String
    
    ' change ##user## to you username
    myPath = "C:\Users\##user##\Documents\"
    
    Dim myDoc As Word.Document
    Set myDoc = myword.Documents.Open(myPath)
    
    myWord.Visible = False
      
    myDoc.SaveAs2 Replace(myDoc.Name, ".docx", ".txt"), fileformat:=wdFormatText
    
    myDoc.Close savechanges:=False
    
    myword.Quit
    Set myword = Nothing

End Sub

If you are a beginner in VBA then I'd also strongly recommend installing the free and fantastic Rubberduck addin for VBA and pay attention to the code inspections.