Use instead the following. You will have to supply the name and path (here - strDocName).
Code:
ActiveDocument.ExportAsFixedFormat OutputFilename:=strDocName, _
ExportFormat:=wdExportFormatPDF, _
OpenAfterExport:=False, _
OptimizeFor:=wdExportOptimizeForPrint, _
Range:=wdExportAllDocument, From:=1, to:=1, _
Item:=wdExportDocumentContent, _
IncludeDocProps:=True, _
KeepIRM:=True, _
CreateBookmarks:=wdExportCreateHeadingBookmarks, _
DocStructureTags:=True, _
BitmapMissingFonts:=True, _
UseISO19005_1:=False