You can't make up your own syntax. The print to PDF does not support file naming from VBA.
You can save a contiguous range using ExportAsFixedFormat (For a single page enter e.g. 2-2 in the input box) e.g.
Code:
Sub SavePageRangeAsPDF()
Const sPath As String = "C:\Path\"
Dim sRange As String
sRange = InputBox("Enter the range of pages to be printed eg 1-3")
If sRange = "" Then
MsgBox "No pages selected!", vbCritical, "Print Pages"
End If
ActiveDocument.ExportAsFixedFormat _
OutputFileName:=sPath & "Robert.pdf", _
ExportFormat:=wdExportFormatPDF, _
Range:=wdExportFromTo, From:=Split(sRange, "-")(0), To:=Split(sRange, "-")(1)
End Sub