Sub testStart()

Dim wdApp As Word.Application
Dim wdDoc As Word.Document

If IsFileOpen("c:\documents\my_file.docx") = False Then 'Word file is not open
    On Error Resume Next
    Set wdApp = GetObject(, "Word.Application")
    If Err.Number <> 0 Then
        Set wdApp = CreateObject("Word.Application")
        wdApp.Visible = False
    End If
    
    Set wdDoc = wdApp.Documents.Open(fileName:="c:\documents\my_file.docx", AddToRecentFiles:=False, Visible:=False)
Else 'Word file is open
    Set wdApp = GetObject(, "Word.Application")
    wdApp.Documents("my_file.docx").Activate
    Set wdDoc = wdApp.ActiveDocument
End If

'move forward with application


End Sub

Function IsFileOpen(fileName As String)
'https://exceloffthegrid.com/vba-find-file-already-open/

Dim fileNum As Integer
Dim errNum As Integer

'Allow all errors to happen
On Error Resume Next
fileNum = FreeFile()

'Try to open and close the file for input.
'Errors mean the file is already open
Open fileName For Input Lock Read As #fileNum
Close fileNum

'Get the error number
errNum = Err

'Do not allow errors to happen
On Error GoTo 0

'Check the Error Number
Select Case errNum

    'errNum = 0 means no errors, therefore file closed
    Case 0
    IsFileOpen = False
 
    'errNum = 70 means the file is already open
    Case 70
    IsFileOpen = True

    'Something else went wrong
    Case Else
    IsFileOpen = errNum

End Select

End Function