The Planetary Defence Force is the standing army of an individual Imperial world, raised and maintained by its planetary governor to defend it against invasion, insurrection and the horrors that stalk the void. Every world in the Imperium is required to muster a PDF, and it is this force that stands as the first, and often the last, line of defence when the enemy comes.
The quality of a PDF varies wildly across the million worlds of Mankind. On a militant hive world it may field disciplined regiments with tanks and artillery; on a backwater agri-world it might be little more than farmers with lasguns and courage. When war escalates beyond their strength, the greater might of the Astra Militarum is summoned, and the finest PDF soldiers are often conscripted into its ranks as tithed regiments to fight across the wider galaxy.
Though rarely glorious, the Planetary Defence Force is the bedrock of Imperial security. They hold the walls, garrison the void ports and buy time with their lives, ordinary men and women standing against extraordinary terror in the Emperor's name.