If you are working in Outlook as your message indicated, you don't need to create an outlook object as you are already working in one.
If you want to insert a text file and format it in the body of a message, then opening it in Word is slow and ponderous. The following is much faster. You can then format the range directly after insertring the text e.g.
Option Explicit
Sub SmokeTestStart()
Dim OutMail As Outlook.MailItem
Dim olInsp As Outlook.Inspector
Dim wdDoc As Object
Dim oLink As Object
Dim oRng As Object
Dim strFilename As String: strFilename = "c:\temp\SmokeStart.txt"
Dim strFileContent As String
Dim iFile As Integer: iFile = FreeFile
Open strFilename For Input As #iFile
strFileContent = Input(LOF(iFile), iFile)
Close #iFile
Set OutMail = CreateItem(olMailItem)
With OutMail
.To = "someone@somewhere.com"
.subject = "This is the subject"
.BodyFormat = olFormatHTML
Set olInsp = .GetInspector
Set wdDoc = olInsp.WordEditor
Set oRng = wdDoc.Range(0, 0)
.Display 'This line is required!
'Insert the text file content
oRng.Text = strFileContent
'Format the range
oRng.Font.Name = "Calibri"
oRng.Font.Size = 11
End With
lbl_exit:
Set OutMail = Nothing
Set olInsp = Nothing
Set wdDoc = Nothing
Set oRng = Nothing
Exit Sub
End Sub