I have the option to buy a hp elitebook folio 9470m from my employer, but previous they clean the harddisk. So I would get the laptop with no operation system on it. My question: Is there a way to reinstall Windows 7 and activate it with the use of OEM certificate?
Obviously, but why don't you read the stickies?? Get latest SP1-U ISO from here, then install HP cert & key by seeing here - especially section 6.F-a & 6.F-b. You can use this too, to automate the process.
If the OEM certificate / product key sticker is still on the machine, that would work too. You just need a copy of the OS media (refer to Tito's post above).