Okay, I keep seeing the same question about the 'Panty Edition' over and over, and the answers vary in their correctness. So I thought I'd write something up. If a mod feels inclined to add it to the OP, that may be useful.
There are three official versions of game released with each update. They are:
Standard Edition (SE)
This version contains the complete story with all the main and side quests. It also has a collectible side-quest which isn't tracked on the quest tracker. For every female NPC in the game, you can find a pair of her underwear someplace (Lily's are in her room, for example). Picking these up will unlock a screen for that character under the 'Panty Collection' menu. Each entry contains some dev notes on the character and the ability to set that character's portrait as the menu screen background.
Panty Edition (PE)
As above, plus several of the entries in the Panty Collection menu have links to view additional bonus scenes. These are all non-interactive masturbation or sex scenes, and are not central to the plot of the story, although they sometimes reference events in it.
These bonus scenes are the only difference between the SE and the PE.
Unencrypted Panty Edition (UPE)
As above, plus all renders in the game are unencrypted, and viewable through the file browser without additional steps.