Assuming the 'generic text' doesn't include any numbers then

Public Sub SaveAttachmentsToDisk(MItem As Outlook.MailItem)

Dim oAttachment As Outlook.Attachment
Dim sName As String
Const sSaveFolder As String = "P:\OUTLOOKDUMP\"
    For Each oAttachment In MItem.Attachments
        If Right(LCase(oAttachment.fileName), 3) = "pdf" Then
            sName = GetNum(oAttachment.fileName) & ".pdf"
            oAttachment.SaveAsFile sSaveFolder & sName
        End If
    Next
End Sub

Private Function GetNum(sText As String) As String
Dim i As Integer
    For i = 1 To Len(sText)
        If Mid(sText, i, 1) >= "0" And Mid(sText, i, 1) <= "9" Then
            GetNum = GetNum + Mid(sText, i, 1)
        End If
    Next
lbl_Exit:
    Exit Function
End Function