Why not include an autoopen macro in Normal's Document Module or an addin that checks to see the file extension and changes the page setup if it hits one of the triggers?
Code:
Sub Document_Open()
On Error GoTo FailWithGrace
Select Case Split(lcase(ActiveDocument.Name), ".")(1)
Case "txt", "log"
With ActiveDocument.PageSetup
.LineNumbering.Active = False
.Orientation = wdOrientLandscape
.TopMargin = CentimetersToPoints(1)
.BottomMargin = CentimetersToPoints(1)
.LeftMargin = CentimetersToPoints(1)
.RightMargin = CentimetersToPoints(1)
.Gutter = CentimetersToPoints(0)
.HeaderDistance = CentimetersToPoints(1)
.FooterDistance = CentimetersToPoints(1)
.PageWidth = CentimetersToPoints(29.7)
.PageHeight = CentimetersToPoints(21)
.FirstPageTray = wdPrinterDefaultBin
.OtherPagesTray = wdPrinterDefaultBin
.SectionStart = wdSectionNewPage
.OddAndEvenPagesHeaderFooter = False
.DifferentFirstPageHeaderFooter = False
.VerticalAlignment = wdAlignVerticalTop
.SuppressEndnotes = False
.MirrorMargins = False
.TwoPagesOnOne = False
.BookFoldPrinting = False
.BookFoldRevPrinting = False
.BookFoldPrintingSheets = 1
.GutterPos = wdGutterPosLeft
End With
End Select
FailWithGrace:
End Sub