I've noticed some kind of designation in certain module names on the site, such as D4, W2, J4 etc.
What are those and what do they mean?
Also, of the adventure modules for sale now, which ones are written for v3.5 and which ones are for the modern Pathfinder rule set?
The letter codes were used mostly on the 3.5 modules. They were a bit of nostalgia, as the old D&D modules used similar letter coding to identify related modules (G1-3, D1-3, Q1, etc.)
In Paizo's case, the letter codes also identified broad themes:
W was for Wilderness
E was for Event
D was for Dungeon
J was for Journey
