From the top Google search result: Yes..

You totally can, but when i did so i encountered this bug that 1/3 times when i killed a demon another exact copy of him would spawn as soon as the first one died. It became a nightmare in the Catacombs... there was this moment that there was more enemies than i could kill.

As I asked another poster in the other thread where you mentioned this, were you using a Doppelganger's weapon at the time? The process of transferring to Hellfire should have stripped you of all your items, forcing you to acquire new ones.

I honestly don't know. I did however get new gear and made it to catacombs, where more enemies spawn as i killed them, there was this instance that were double the initial enemies. It was too much and just deleted the character and started a new one directly from hellfire.

Doppelganger's is qlvl 11, so you could have acquired it starting on dlvl 6.