@Stewie Mac: I tried to do that with Hilton Iru Fushi Maldives. Impossible. Their phone line condition seems so weak, that you can hardly hear them. They were not very responsive on the emails either and HHonors call center said that only hotel can combine pts with cert. Maybe it was me, but I had no luck in doing this, so I booked for pts eventually.

As Hilton sent me a new certificate, I decided not to wait for the expiration time this time. So I booked a standard room at Hilton Vienna Plaza (€199 / night) and showed the certificate. They looked at me like I would came from the moon and said it is most probably not possible to pay with this piece of paper. They had to call US to check with them to finally let me know it is possible to pay with this... piece of paper.

I prefer points. At least this is hassle free experience.