Ledge Campaigns use the Pathfinder rules by default, with D&D 3.5 content converted to these rules.  Players wanting to use D&D 3.5 content can review the Pathfinder Roleplaying Game Conversion Guide for specifics, but a few general rules / clarifications are provided below:

• When converting D&D 3.5 content, skill requirements should be reduced by 3 (to a minimum of 1).
• All fighter bonus feats from D&D 3.5 count as Combat feats in Pathfinder.  Other feats may be eligible if they're clearly intended to be combat-oriented feats.
• If new mechanics rehash old mechanics and they could conceivably be compatible, assume that they are compatible.  For example, chakras from Magic of Incarnum can be updated to those in Akashic Mysteries through a relatively straightforward process.  However, the Inspiration mechanic of Factotums would not naturally convert to the Inspiration mechanic of Investigators, despite several similarities.