Isso deve ajudar. Observe que o get-childitem procura o doc * e o regex na substituição.
$Files=GET-CHILDITEM 'C:\Users\Ashley\downloads\articles\*.DOC*'
$Word=NEW-OBJECT –COMOBJECT WORD.APPLICATION
Foreach ($File in $Files) {
# open a Word document, filename from the directory
$Doc=$Word.Documents.Open($File.fullname)
# Swap out DOCX with PDF in the Filename
$Name=$Doc.Fullname -replace('doc([x]{0,1})',"pdf")
# Save this File as a PDF in Word 2010/2013
$Doc.saveas([ref] $Name, [ref] 17)
$Doc.close()
}