Convert Batches Of Doc Files To PDFs - Add A Filter To FileDialog

Set up a quick piece of code to convert batches of .doc files to .pdfs

Question 1 : What is the proper syntax to add a filter to the FileDialog to only allow for .doc and .docx files

Code:
Sub DocTOpdf()
Dim s As Variant
Dim Res As Integer
Dim oWord As Object

[Code] .....

Question 2: It would seem that randomly when running the code a Run-time error -21467259 (80004005) occurs at

Code:
oWord.ActiveDocument.ExportAsFixedFormat OutputFileName:= _
s & ".pdf", ExportFormat:=wdExportFormatPDF, _
OpenAfterExport:=False, OptimizeFor:=wdExportOptimizeForOnScreen, Range:= _
wdExportAllDocument, From:=1, To:=1, Item:=wdExportDocumentContent, _
IncludeDocProps:=True, KeepIRM:=True, CreateBookmarks:= _
wdExportCreateNoBookmarks, DocStructureTags:=True, BitmapMissingFonts:= _
True, UseISO19005_1:=False