You hav eto have a copy of the I-140 approval notice. So, politely ask the HR or the lawyer to give you a photocopy and normally they will give it to you.
If you can not get the copy of the I-140 approval notice, but your have a copy of the old I-140 receipt, it may also work. Or If you do not have the receipt, but you have the receipt#, you may just print out the online approval status information and provide it as the proof of PD when filing I-485 based on the new I-140 when the PD is current and it may work because USCIS can find your case status based on the receipt#.
