Presumably PDF is a pre-existing sub folder of the original folder in which case
Code:
While Len(strFilename) <> 0
Set oDoc = Documents.Open(strPath & strFilename)
strDocName = ActiveDocument.Name 'Use Name not fullname
intPos = InStrRev(strDocName, ".")
strDocName = Left(strDocName, intPos - 1)
'This instruction converts to PDF
strDocName = strDocName & ".pdf"
oDoc.SaveAs FileName:=strPath & "PDF\" & strDocName, _
FileFormat:=wdFormatPDF 'add the path
oDoc.Close SaveChanges:=wdDoNotSaveChanges
strFilename = Dir$()
Wend
If you want to create the folder then see the Createfolders function at
https://www.gmayor.com/useful_vba_functions.htm where you will also find code to ensure the filenames are unique to avoid overwriting duplicated names.