Hi , entry permit to HK

Hi ,i am currently living here in phils, I have a friend who works in hk ,then he wants me to visit hk ,he made an invitation letter ,but then my question is do he need to phil hongkong embassy so his invitation can be valid ?but then if he send me his invitation with out stamp of embassy it still valid ?can I fly ?
What I mean is do he still need to go phil-hk embassy ?