If you prefer "humanity's finest" in heavy void-armor, the Solar Auxilia rules offer everything from massive tank squadrons to disciplined infantry cohorts. You can find detailed breakdowns of their strategies and Solar Auxilia color schemes through community hobby guides. Imperialis Militia
If you are searching for the Liber Imperium PDF, it typically refers to one of two different rulebooks associated with the Warhammer 40,000 The Horus Heresy universes. liber imperium pdf