A card with two faces always enters play as the front face. Whenever it is not in play, it is considered to be the front face. When a game effect instructs you to flip it, it is transformed into the card on its other face, and loses all abilities and attributes on its other face.

Whether a card is rezzed/derezzed is independent from whether it is flipped/unflipped. So if Patent Acquisition is scored and flipped into Injunction, then derezzed, if it is later rezzed again it would be as Injunctoin. This is because derezzing a card does not cause it to leave play.

If Injunction is trashed while installed (for example, via Knifed or Parasite), it will enter Archives as Patent Acquisition. The Runner can therefore steal it by running Archives and accessing it normally.